After completion of this chapter, the physical therapist should be able to do the following:
Recognize/identify the general anatomic, physiologic, and neuromuscular differences that exist between genders.
Develop an understanding of common gender differences that predispose the female athlete to development of patellofemoral dysfunction.
Identify characteristics that may contribute to increased susceptibility of the female to anterior cruciate ligament (ACL) injury, including mechanism of injury, intrinsic factors, extrinsic factors, and combined factors.
Identify typical muscular activation and timing patterns, as well as the kinematics and joint position of the lower extremity during performance of physical tasks by females.
Educate physically active females, coaches, and other sports medicine personnel regarding prevention of ACL injuries, including proper cutting and jumping techniques and neuromuscular reeducation/strengthening of the lower extremity.
Prescribe a lower-extremity reactive neuromuscular training exercise program for the physically active female to aid in ACL injury prevention.
Identify possible sequelae to ACL injury and rehabilitation.
Utilize the concept of “envelope of function” to minimize adverse effects of musculoskeletal injury and subsequent rehabilitation.
Understand the importance of incorporating core strengthening into an exercise program of the physically active female.
Identify the potential stresses and risks that occur in the shoulder joint complex as a consequence of softball windmill pitching.
Prescribe an exercise program specific to the windmill softball pitcher.
Understand the potential stresses to the shoulder complex during freestyle swimming and identify which musculature is at greatest risk for fatigue and subsequent impingement.
Develop a comprehensive rehabilitation program for the swimmer with a shoulder injury.
Develop a general understanding of most common injuries sustained by female gymnasts and identify potential risks involved in the excessive training at an early age common among female gymnasts.
Acknowledge the implications that excessive, early training may have on hormonal and growth processes in the young female athlete.
Describe the components of the female triad to enable prevention, identification, and treatment of these components as a member of a multidisciplinary medical team.
Educate physically active females in proper exercise guidelines when planning for, during, and after pregnancy with a thorough knowledge of the physiologic changes that occur during this unique time.
The visibility of the athletic female, which has grown dramatically over the past century, is now established throughout the world. At the beginning of the century, in 1902, the modern Olympic Games were founded, but women were excluded from participation. At that time, women’s sports were considered to be “against the laws of nature.”212 In 1972, Title IX of the Educational Assistance Act was passed. This was a pivotal point in the history of the United States regarding female participation in sports and exercise. Title IX states that “no person in the U.S. shall, on the basis of sex, be excluded from participation in, be denied the benefits of, or be subject to discrimination under any educational program of action receiving federal financial assistance” 212, p. 841 After Title IX, a 600% increase was seen in all levels of women’s athletic participation.211 Women and girls of all ages and abilities are participating in sports in record high numbers. In fact, 43.2% of collegiate athletes5 and approximately 46% of Olympic athletes3 were female as of publication of this text.
Participation in sports by girls and women continues to grow. The National Federation of State High School Associations has collected data on sports participation across the United States since 1971.6 In its most recent school year report, the National Federation of State High School Associations reports 7,692,520 scholastic (high school aged participants) (both male and female), the greatest number of participants ever. Likewise, the total number of females participating set an all time high with 3,207,533 participants.6 Basketball remains the most popular high school sport for girls in the United States, with almost 18,000 participants, followed by track and field/cross country, volleyball, softball, and soccer.6
Studies by the National Collegiate Athletic Association (NCAA) describe a 10% increase in participation across athletic programs for women from 1989 to 1993.24 The greatest single rise in female participants of 21.18% occurred during the 1982-1983 school year, as compared to a 5.85% increase in male participants.6 The NCAA reports that more than 100,000 women participate in intercollegiate sports each year; in fact, this number is fast approaching 200,000.5 The most recently available participation report indicates that 195,657 women participated in collegiate sports (43.2% of all participants), with the greatest number participating in soccer, followed by track and field, softball, and basketball. Currently, women play in a wide variety of sports, play at many levels, are offered the opportunity not only to participate but also to gain monetary reimbursement (scholarship and professional salaries) and media acclaim. As participation and notoriety has increased, so has the need to understand the injuries being sustained by female athletes.
With the increase in women’s participation in sport came an increased injury incidence among female athletes.43 It was common, even 15 years ago, for a female athlete to receive different treatment than a male with an identical injury. For example, women runners who complained of tendonitis were often told to stop running, whereas men were given a specific treatment protocol that combined rest with activity. This is no longer commonplace. No longer are male athletes predominant recipients of rehabilitation. Active females are being rehabilitated as frequently as active males. There has been some suggestion that females are more susceptible to athletic injury than males176; however, current literature indicates that injury patterns are more sport-specific than gender-specific.212,249 Nonetheless, there are several types of injuries, which seem to be more prevalent in the female athlete. Such injuries are of increasing concern to the sports medicine specialist.
One heavily researched area in the sports medicine arena is the increased rate of anterior cruciate ligament (ACL) injury among females when compared to males.212,237,270 Female athletes have a 4 to 6 times higher incidence of ACL injuries compared to their male counterparts.133,206 Other injuries found to be frequent among female athletes include patellofemoral pain syndrome, spondylosis and spondylolithesis, stress fractures, bunions, and shoulder pain.16,32,43,80,85,158,229,252 The reasons for the high frequencies of these types of injuries in females remain elusive but have been receiving more attention in the last decade. The media, medical, and rehabilitation communities have brought female ACL injuries and the female athlete triad to the forefront of attention (see later section “The Female Athlete Triad”). A discussion regarding basic gender differences serves as a basis for further discussion of injuries common to representative, individual sports, as well as other considerations regarding the active female.
Physiologic Strength Differences
Gender differences between females and males are evident in strength, aerobic capacity, and endurance. These differences become pronounced after puberty. Prepubertal boys and girls have similar strength, and when corrected for lean body mass, and their max is also similar.250,256 Endurance performance is just slightly better in boys than in girls before puberty. However, these differences may be a result of social rather than biologic constraints, including the possibility of fewer role models for girls, less opportunities, and different training programs.212,256 At puberty, these gender-related discrepancies are exaggerated because of both anatomical and physiologic differences. This time period seems to be a time when female athletes are particularly at risk, as a result of the hormonal, biomechanical, and functional performance changes that occur.109,252
Skeletal muscle physiology in men and women does not differ significantly.251 Testosterone and androstenedione are the androgenic hormones that are most important in muscle fiber development. There is a variance in resting testosterone levels, but the average for females is between one-tenth and one-half the blood levels of males. Consequently, men have greater potential for strength and power development related to testosterone levels alone. When considering estrogen levels, women have higher levels than men, and this hormone interferes with muscular development as a result of its role in increasing body fat stores. After puberty, women typically have less lean body mass than men, especially in the lower body, because of increased estrogen levels, and subsequent fat body mass increases.88 Average body fat for a sedentary college-age woman is 23% to 27%, whereas for a college-age man it is 15% to 18%. It is typical for some athletes (especially runners, gymnasts, and ballet dancers) to demonstrate lower body fat percentages because of the performance and appearance demands of their sports. These two physiologic hormonal differences (body fat and blood hormone levels) help to explain why muscle mass is predictably lower in women than in men.88,275
Strength can be examined in 2 different ways. Absolute strength is the maximum amount of weight one can lift (e.g. 50 lb). Relative strength relates this maximal amount to an individual’s muscle mass (e.g. 80 lb of muscle mass can lift 50 lb).141 Men appear to demonstrate larger absolute strength gains as a consequence of larger cross-sectional muscle fiber size. However, the actual number of muscle fibers is similar between genders. When examining relative gains in strength, studies show that women and men achieve similar results while undergoing identical weight-training programs.141,196 “Because muscle cross-sectional area (muscle fiber size multiplied by the number of muscle fibers) is directly related to the ability to produce force, individuals who have larger muscles are able to lift more weight.”196, p. 4 Table 31-1 provides examples of this conclusion.
Table 31-1Relative Versus Absolute Strength in Female Versus Male Athletes ||Download (.pdf) Table 31-1 Relative Versus Absolute Strength in Female Versus Male Athletes
|Female soccer player 125 lb || |
With 15% body fat = 106 lb lean body mass
Absolute strength = 150 lb squat
Relative strength = 150/106 = 1.4
|Male soccer player 155 lb || |
With 12% body fat = 136.5 lb lean body mass
Absolute strength = 185 lb squat
Relative strength = 185/136.5 = 1.4
When comparing strength to lean body mass (body weight without fat) or cross-sectional area, women are about equal to men and are equally capable of developing strength relative to total muscle mass.196 Gender is irrelevant in the ability of a muscle to produce force.196 Holloway and Baechle141 were unable to show significant gender differences in adaptations to resistance training, except for the amount of muscle hypertrophy. Absolute strength gains are a result of the combination of muscle hypertrophy and neuromuscular recruitment. When diet is unchanged during a resistance training program, the average woman responds with a decrease in intramuscular and subcutaneous fat stores, and little change in limb circumference (less hypertrophy than males) mostly owing to lower testosterone levels and smaller muscle fiber size.141,196,212 True muscle hypertrophy is less visible in females, but improved muscular definition is evident.196
Dore et al88 found that males and females exhibited similar cycling peak power until age 14 years. At age 14 years, loosely considered to be the transition to puberty, males demonstrated higher cycling peak power. Males had higher lean leg volume than females. As age increased, where there were similar lean leg volumes, males still showed greater cycling peak power. Conclusions were twofold: (a) the sex-related difference can be explained by the difference in body composition, specifically there is a lower limb fat increase in girls, whereas there is an increased lean body mass in boys; and (b) the question of the possibility that differences in neuromuscular activation exist, which could play a role in peak muscle performance.88 Neuromuscular differences are examined more thoroughly later in this chapter, in the section entitled “Neuromuscular Differences”.
So far, no evidence exists to suggest that women should undergo strength training any differently than men. “Assuming equal nutrition, the rate and degree of improvement in strength should be equal between genders. Significant gains in muscle strength and endurance can be achieved by use of a training program 3 to 4 days a week.”196, p. 5 Once either gender has reached a high level of competitiveness and muscularity, changes in muscle mass and fiber content is minimal.17 However, women do show lower proportions of their total lean body mass in their upper body, contributing to gender strength differences that are greater in the upper body than in the lower body. Nevertheless, hypertrophy and absolute strength differences evident between genders occur as a result of the physiologic changes that occur at puberty.196
Anatomical differences are also a reason for variance in strength. Men and women’s bodies respond differently to similar weight training programs as a result of anatomical differences. These differences include women are 3 to 4 inches shorter; are 25 to 30 lb lighter; have 10 to 15 lb (8% to 10%) more body fat; have 40 to 45 fewer pounds of fat-free weight (bone, muscle, organs); have less muscle mass supported by narrower shoulders; and have shorter extremities.196 “All these factors combined give men a mechanical advantage over women, which enables them to handle more weight and generate more power.”196, p. 3 Broader shoulders tend to benefit males in developing muscular strength in the upper body, whereas wider pelvises seem to benefit females in developing lower body strength. Men with broader shoulders have a higher center of gravity than women with wider pelvises, giving men a superior mechanical advantage for gaining upper-body mass.196 Thus, as previously stated, the largest difference in absolute strength in females versus males is found in the upper body as compared to the lower body.141
Structural differences have been noted between genders in both the upper and lower extremities. In the upper body, structural differences include narrower shoulders, shorter arm lengths, decreased muscle fiber, and total muscle cross-sectional area, and according to some authors, increased carrying angle of the forearm.196,250 When examining structural differences of the lower extremity between genders, multiple factors affect alignment. Women have greater amounts of static external knee rotation, greater active internal hip rotation, greater interacetablular distance, and increased hip width when normalized to femoral length than men.65 These factors contribute to greater knee valgus (genu valgum) angles in women. The structural combination of increased hip adduction and rotation, femoral anteversion, and genu valgum may explain the larger quadriceps (Q) angle and rotational positioning of the lower extremity in women than in men (Figures 31-1 and 31-2). The average Q angle for men is 13 degrees and for women it is 18 degrees,61 but measurement of the Q angle is examiner dependent and can be erratic. Lower-extremity structural differences may play a factor in lower-extremity injuries in the active female.65 Structural differences related to ACL injury are discussed in greater detail later in this chapter, in section entitled “Intrinsic Factors”.
Structural differences between men and women
Women (left) typically exhibit a wider pelvis, femoral anteversion greater tibial external rotation, and genu valgum. (Reproduced from Griffin LY. Rehabilitation of the Injured Knee. St. Louis, MO: Mosby-Year Book; 1995, with permission from Elsevier.)
Gender differences in Q angle
Women (right) exhibit a greater Q angle, increased external tibial torsion, and femoral anteversion. (Reproduced from Griffin LY. Rehabilitation of the Injured Knee. St. Louis, MO: Mosby-Year Book; 1995, with permission from Elsevier.)
As previously mentioned, the larger Q angle found in females has been identified as a predisposing factor to patellofemoral dysfunction, which plagues many active females regardless of sport or age. Anterior knee pain is one of the most common sources of complaint among female athletes.41 Most patellofemoral dysfunction can be categorized as mechanical or inflammatory, with the rare exceptions of tumors, regional pain syndrome, and referred pain patterns.147 For the active female, patellofemoral dysfunction should be thoroughly evaluated to determine whether instability, malalignment, tracking abnormalities (either of the patella itself or the femur underneath it), compression forces, or motor control issues contribute to the anterior knee discomfort. Appropriate patellar mobility should include sufficient superior glide with active quadriceps contraction, as well as equal medial and lateral glide.235 Increased patellar lateral glide indicates abnormal laxity and instability when correlated with a positive apprehension test that simulates instances of patellar subluxation or dislocation.147,235 Patellar instability is a mechanical cause of anterior knee pain and occurs more frequently in females than in males.147 The active female is more susceptible to patellar instability secondary to the anatomical alignment and muscular strength differences already described. However, contemporary thinking supports more a biomechanical and motor control approach to both the genesis and treatment of patellofemoral syndromes and anterior knee pain.54 Treatment of patellar instability and other patellofemoral diagnoses have been discussed in much greater detail in Chapter 24.
Alignment observation should include not only Q-angle measurements but also determination of tibial torsion, foot position, and leg-length discrepancies. Malalignment may include superior or inferior position of the patella, medial or lateral patellar glide, rotation, or tilt. Abnormal positions of the patella may include 1 or a combination of these factors.190 Common patellar malalignment patterns include “grasshopper” or “squinting” patella. A complete evaluation of muscular balance, including both flexibility and strength of the hip, pelvis, and thigh musculature, directs treatment to minimize these suboptimal patterns.190 McConnell patellar taping191 or the use of kinesiotape applications29 may provide proprioceptive input to affect patellar tracking and muscular recruitment. These interventions provide symptomatic relief in many patients, which allows for a conservative rehabilitation program to be completed.191
A static Q-angle measurement is not as helpful as the same measurement before and during an activity such as a minisquat to determine if the Q angle increases, demonstrating lack of optimal motor control.147 Patellar tracking should be assessed to ensure normal position of the patella within the trochlear groove throughout knee motion. An example of abnormal patellar tracking is a J sign, when the examiner observes the patella jump laterally (at approximately 30 degrees of flexion) as the knee moves from flexion into extension and is associated with patellofemoral symptoms.178,235 Conservative management of patellar tracking abnormalities, especially in the adolescent female athlete, should be the rule147 and should be addressed systematically after a thorough evaluation of the muscle imbalance for flexibility and strength. Neuromuscular training to address recruitment patterns of both proximal and thigh musculature, core stability, and balance deficits are elaborated upon later in this chapter. Techniques to be discussed have applicability with the rehabilitation program for most biomechanical causes of anterior knee pain.
This discussion of patellofemoral dysfunction illustrates the increased predisposition to this injury complaint of the physically active female based on the gender differences in anatomy and strength. A subsequent review of the neuromuscular differences precedes the discussion of another widespread knee injury that is more common in female than in male athletes.
When comparing genders, research supports differences in dynamic neuromuscular control of lower limb biomechanics.129,130,133,218,295 Neuromuscular control is a combination of proprioception and the muscular systems’ response to the proprioceptive input. Imbalances in quadriceps-to-hamstring ratios, differences in jump-landing positions, weakness in proximal hip musculature, higher landing forces, and lower gluteus maximus electromyographic (EMG) activity during landing are all reported in females when compared to males.132,145,295 Noyes et al218 conducted research using the drop-jump test with both male and female athletes that measured the distance between the hips, knees, and ankles in the coronal plane during landing. Findings revealed no significant difference between male and female subjects in mean knee and ankle separation distance during the landing and takeoff phases. Significant differences between male and female athletes were shown in knee and ankle separation during the prelanding phase only (the 3 phases include takeoff, prelanding, and landing). However, after a 6-week Sportsmetrics neuromuscular training program128 (Appendix A), female athletes had statistically greater knee and ankle separation distances than those of males in all 3 phases of the jump-land sequence.207
Hewett et al130 went beyond the coronal plane and measured a drop jump-landing task in females with 3-dimensional motion analysis. Data were gathered on athletes prior to sports participation. Athletes who had injured their ACL demonstrated significantly higher knee abduction angles (knee valgus) at initial contact and increased maximal limb displacement than did those who were uninjured. Peak vertical ground reaction force corresponded with knee abduction angle. The greater the abduction angle, the greater the ground reaction force in ACL-injured athletes but not in uninjured athletes. Athletes who sustained ACL injuries “demonstrated significant increases in dynamic lower extremity valgus and knee abduction loading before sustaining their injuries compared to uninjured controls.”130, p. 497 Maximum knee flexion angle at landing was 10.5 degrees less in injured than in noninjured athletes. These differences suggest decreased neuromuscular control or alternative strategies for function in the lower extremity of females as evidenced by biomechanical differences observed.12,30
Coactivation of the quadriceps and hamstrings is an important protective mechanism at the knee joint for protection against not only excessive anterior shear forces but also knee abduction and dynamic lower-extremity valgus forces.34 Female athletes have lower hamstring-to-quadriceps-strength ratios than males during isokinetic testing at 300 degrees per second.129 When the hamstrings are underrecruited, relative overrecruitment of the quadriceps may result. This recruitment strategy used by females may directly limit the potential for balanced muscular cocontraction, which aids in protecting ligaments.130 It has also been postulated that males may use a protective mechanism involving the hamstrings, considered to resist anterior tibial translation, to counteract high-peak landing forces. Females tend to contract their quadriceps first in response to an anterior tibial translation, which provides additional anterior translation, whereas males responded by contracting their hamstrings first, thereby limiting the anterior translation. With these findings, it is suggested that females tend to be “ligament-dominant” in their joint strategies, whereas males demonstrate more “muscle-dominant” joint strategies.133
Greater knee abduction angles during jump-stop unanticipated cutting activity were also described by Ford et al.105 Females demonstrated greater knee abduction angles (knee valgus) at initial contact than their male counterparts. Greater knee abduction angles support the concept of ligament dominance rather than muscular control to absorb the ground reaction force during sporting maneuvers. In such a movement strategy, the athlete is allowing the ground reaction force to control the direction of motion of the knee joint, which, in turn, causes the ligaments to take up a disproportionate amount of force.105
Proximal hip musculature activation is also found to differ between genders. Zazulak et al295 reported that female athletes demonstrated less activity of the gluteus maximus compared to males during the landing phase of a single-leg drop jump. Decreased activation of proximal hip stabilizers may contribute to the valgus landing position observed in female athletes. Greater rectus femoris activity was also observed in females compared to males during the precontact period of the jump. This is postulated to place an increased anterior sheer force on the tibia during landing. The authors concluded that these 2 findings together may contribute to altered kinetic energy absorption during landing, as well as causing increased ground reaction forces and high valgus torques contributing to knee injury.295
Female sex hormones may also have significant effects on neuromuscular control. Estrogen has both direct and indirect effects on the neuromuscular system. During the ovulatory phase, there is a slowing of muscle relaxation. Throughout the menstrual cycle, estrogen levels fluctuate radically. Fluctuating hormone status has profound effects on muscle function,253 tendon and ligament strength, and the central nervous system.133 Hormonal influences on neuromuscular control is discussed further in the ACL section of this chapter. Clearly, neuromuscular patterning and performance is affected by many factors.
Anterior Cruciate Ligament Injuries
With higher participation rates of females at all levels, increased sport-related injuries were expected; however, what was unexpected was the disproportionate number of knee ligament injuries that occur. The most serious injury that has risen to the forefront of attention is injury to the ACL of females. A pattern of disproportionately high ACL injury rates in females, compared to their male athlete counterparts, was identified. For example, during the 1989-1990 intercollegiate basketball season, the NCAA Injury Surveillance System data showed that female athletes injured their ACLs 7.8 times more often than males,228 and this trend continues. Sports that appear to have high risk, at all levels of play, involve jumping, rapid deceleration, and cutting maneuvers. Sports such as soccer, basketball, volleyball, team handball, and gymnastics have been identified as high-risk sports for the female athlete.24,25,44,63,71,87,103,115,127,132,171,180,195,222,247,261,296,298 In fact, more than 30,000 serious knee injuries in female athletes at the high school and intercollegiate levels are projected to occur yearly in the United States.125
The costs of ACL injuries are dramatic, not only financially (medical and rehabilitation services) but also in terms of long-term consequences, such as concurrent injury (such as articular cartilage or meniscus), lost playing time, lost scholarships, and increased potential for long-term posttraumatic osteochondral degeneration and disability.112,119,289 According to Ireland,148,150 even in the era where prevention has been deemed important, females continue to experience a higher rate of injury to the ACL than their male counterparts. What is especially troubling is that even as years have passed and female athletes begin sports play earlier, train harder, and receive improved training and coaching, their injury rate has not declined.150 Therefore, the present focus remains less on reporting injury statistics and hypothesizing about potential causes and continues in the era of prevention. Prevention of ACL injuries in the female athlete has become a priority for the sports medicine, rehabilitation, and research communities.
As more women and girls participate in sports, much attention has been given to understanding the mechanisms of ACL injuries. Many authors have described 2 mechanisms of injury: contact and noncontact.24,25,146,218 Approximately 30% of all ACL injuries are classified as contact injuries, and the remaining 70% are not related to direct contact and classified as noncontact.119 Some authors have reported that as many as 75% of sports-related injuries to the ACL are via noncontact mechanisms.219 Contact injuries are easily discerned from the clinical history surrounding the injury and typically occur during contact sports like football and rugby. In contrast, the mechanisms and activities that are involved in noncontact ACL injuries are less apparent and vary between sports. Sports that are at high risk for, and incur, many noncontact ACL injuries are those classified as noncontact or collision sports such as basketball, soccer, volleyball, gymnastics, and team handball.23,25,31,111,150,283
Early writing by Henning in the late 1980s influenced much of the current thinking about the mechanisms of noncontact ACL injuries.119 After studying injuries incurred by female basketball players over a 10-year time span, Henning concluded that the 3 most common mechanisms of injury were119:
Planting and cutting (29% of all injuries)
Straight-knee landings (28% of all injuries)
One-step stop with the knee hyperextended (26% of all injuries)
Henning concluded that prevention and skill development (especially in the female athlete) must incorporate the opposite of the previously mentioned motor behaviors, including:
These motor behaviors are addressed more thoroughly later in the chapter in the section on prevention and training.
Subsequently, many mechanisms have been described for contributing to noncontact injuries, including sudden forceful twisting motions with the foot planted,194 planting/sidestepping/cutting maneuvers,77 “out of control play,”119, p. 142 landing,49,103 and deceleration maneuvers.119 Video analysis of ACL injuries that occurred during the play of basketball and soccer demonstrated that women were injured most commonly when landing from a jump and when they suddenly stopped running.119 It is very interesting to note that women and girls have been shown to perform landing and cutting activities with more erect posture than men, and therefore place themselves at greater risk for ACL injury.119 Video analysis of actual ACL injuries demonstrated that the position of the lower limb at the time of injury is often knee flexion less than 30 degrees, a position of knee valgus, and external rotation of the foot relative to the knee (Figure 31-3).49,119,128
Typical position of ACL injury
Note that knee valgus, foot external rotation, and knee flexion are less than 30 degrees.
Postural and positional variations in motor skills, when combined with greater valgus alignment and increased quadriceps activation, may further increase the possibility of injury for the female athlete.132 Total positional control of the lower extremity is important, both in terms of flexion/extension and varus/valgus. Low flexion angles (commonly described as less than 45 degrees flexion) increase the anterior strain on the ACL when active quadriceps contractions occur. The quads act as the ACL antagonist and add to the anterior/posterior straight plane load sustained by the ACL. Likewise, increased varus/valgus positioning of the lower extremity adds torque to the knee that challenges the ACL in its derotational function. Factors to explain the position of the lower extremities of females during landing may include deficits in proximal muscle strength and endurance as well as neuromuscular skill factors.
Finally, related to impact during landing, current research suggests that strategies differ in females as compared to males. This may be a result of biomechanical factors, poorer muscle strength and/or neuromuscular control, or insufficient strategies for shock absorption, as previously discussed.169 Dufek and Bates94 examined the relationship between landing forces and injury stating that many injuries that occur during jumping sports occur during landing. Male athletes appear to employ different mechanisms to compensate for high landing forces than do females.129,132 Markolf et al186 demonstrated that muscular contraction can decrease both the varus and valgus laxity of the knee when landing. Jumping and landing are addressed in greater detail in a later section entitled “Knee Kinematics and Landing Characteristics”.
In summary, although women do sustain contact mechanism ACL injuries, the vast majority appears to occur by noncontact mechanisms. According to the Hunt Valley Consensus conference,119 “The common at-risk situation for noncontact ACL injuries appears to be deceleration, which occurs when the athlete cuts, changes direction, or lands from a jump.”119, p. 149
Although many studies offer strong support for noncontact mechanisms of injury as prevalent in the female athlete,25,118,180,207,208,279 Ireland maintains that the “true incidence of noncontact ACL injuries and the actual numbers of athletes affected are difficult to determine.”150, p. 150 The discrepancy between ACL injury rates by sex and mechanism of injury, at all levels of sport participation, remains a hot topic in sports medicine. Fortunately, neuromuscular control, balance, and motor skill training all appear to be critical modifiable factors associated with injury prevention.
Factors Related to Anterior Cruciate Ligament Injury in the Female Athlete
Why women continue to sustain 2 to 8 times more ACL injuries than their male counterparts continues to be an unanswered question for researchers in many disciplines. Clearly, injuries to the ACL occur as a result of complex interactions of anatomical, biomechanical, neuromuscular, hormonal, and environmental factors. Various factors have been suggested to explain these differences and are categorized by many authors as intrinsic (factors that are not controllable) and extrinsic (factors that are controllable).22,24,118,124,146,150 More recently, a third category of factors, described as “both” or partially controllable has been described by Ireland (Table 31-2).150
Table 31-2Summary of Factors Suggested to Contribute to ACL Injury in Female Athletes ||Download (.pdf) Table 31-2 Summary of Factors Suggested to Contribute to ACL Injury in Female Athletes
|Intrinsic Factors ||Extrinsic Factors ||Combined Factors |
Physiologic rotatory laxity
Notch size and shape
Muscular firing order
Kinematics of movement (See Figures 31-4, 31-5, 31-8, and 31-10A, B)
Intrinsic or noncontrollable factors have been described as hormonal effects of estrogen, inherent ligamentous laxity present in females, and other anthropometric differences in men and women, such as lower-extremity alignment, notch width, and ACL size.
Investigation regarding notch width and ACL size has demonstrated females to have smaller notches and smaller ACLs than males22,144,269,279; however, the evidence correlating this with injury is contradictory.133 Regardless, there is little or no opportunity for reasonable intervention, and these areas have been researched less in the last several years. Likewise, although laxity is greater in females than in males,248 there is conflicting evidence regarding the relationship of laxity to injury. Exercise-induced laxity that occurs after 30 minutes of athletic activity may play a role in ligament injury and relate to neuromuscular protective training.272 Finally, investigations of Q angle in relationship to injury demonstrate that injury rate differences between males and females could not be accounted for by the differences in anatomy.118
Research efforts have been dedicated to understanding the interaction between female sex hormones and ACL injuries. Because the female sex hormones estrogen, progesterone, and relaxin are cyclical and affect ligaments, they may play a role in fluctuation in both strength and laxity of the ACL.133,289 Conflicting research evidence exists as to what portion of the menstrual cycle is the most “risky,”25,26,288,289 and whether the effects of hormones (estrogen, especially) may be greater than just on the ligament itself and may extend to changes in motor skill.133,236 Originally, the ovulatory phase was described as the time during which most injuries occurred.289 More recently, Slauterbeck and Hardy263 found that many injuries occurred around menses. In their most recent work, Wojtys et al288 described that more ACL injuries than expected (43%) occurred during the ovulatory phase (in all females) and fewer injuries than expected occurred during the luteal phase (34%). The distribution of injury by phases was different for those women who were taking oral contraceptives, with only a trend toward more injuries in the ovulatory phase (29%), and fewer injuries than expected during the follicular phase (14%), demonstrating the potential for some protection offered by use of oral contraceptives. Möller-Neilson and Hammer199 also reported decreased injury rates in women who used oral contraceptives.
The effects of hormones may extend beyond their effect on the ACL itself. Evidence suggests that the neuromuscular system may be significantly affected by the fluctuating milieu of female sex hormones.133,166 Estrogen may have effects on neuromuscular patterning and performance throughout the menstrual cycle, but seems to decrease motor skills in the premenstrual phase.175,236
Clearly, the relationship between female hormones and ACL injuries remains controversial, not only in terms of susceptibility of ligaments to injury but also in terms of mechanism and location of action. It is not clear whether hormones influence muscle function and motor skills,236 the neuromuscular system,133,175,230 or cerebral/central nervous system function.165,236,288 Interestingly, over the last several decades, suggestions for control of intrinsic factors have been given, such as notchplasty and hormonal manipulation for protection of the ACL in females. These examples were not received with much zeal by the medical community and were never accepted as reasonable interventions. Most in sports medicine agree that to reduce the number of ACL injuries sustained by the female athlete, attention must be paid to factors that are modifiable,150 such as extrinsic or combination factors.
Extrinsic or controllable factors are parameters such as leg strength (both total absolute strength and hamstrings/quadriceps ratios), muscle recruitment order, muscle reaction time, playing style, training/preparation, coaching/conditioning, skill acquisition, and surfaces of play.146,150,290
Generation of muscular force is a key element in providing dynamic stability about joints. The inability to control external forces may result in injury to the static structures providing stability to that joint. The inherent physiologic differences in muscle mass and hormonal levels of testosterone between males and females make it predictable that males will always be stronger than females. If body mass is accounted for and subjects of similar activity levels are compared, does this inequality still exist?
Huston and Wojtys145 tested this hypothesis using isokinetic testing and concluded that athletic females and a control group of females were both statistically weaker in quadriceps and hamstrings muscle strength at 60 degrees per second, as compared to their male counterparts. Other researchers have also documented that women have less muscle strength in the quadriceps and hamstrings than men, even when normalized for body weight.122 Anderson et al22 also tested the quadriceps and hamstrings isokinetically at 60 and 240 degrees per second and found similar results. With corrections for body mass, the male athletes generated greater peak torque, greater work, and average power outputs than the female athletes for both quadriceps and hamstrings (p < 0.05).22 Knapik et al158 determined that female athletes with a hamstring muscle group more than 15% weaker than the other side were 2.5 times more likely to sustain a lower-extremity injury. They also reported that this side-to-side imbalance in hamstring strength existed in 20% to 30% of female athletes.
Previous research illustrates the importance of hamstring strength and endurance in acting as an agonist to the ACL for dynamic knee joint stability.22,90,145,247 The hamstring muscles have been shown to be protective of the ACL because of their ability to shield the ACL from excessive anterior shear and strain. If the hamstrings are to effectively counteract the torque produced by the quadriceps, they must demonstrate a certain percentage of strength as compared to the quadriceps they are opposing. Knapik157 also reported that athletes with a hamstring-to-quadriceps ratio of less than 0.75 were 1.6 times more likely to be injured. Isokinetic testing by Moore and Wade200 revealed that hamstring-to-quadriceps ratios in females were significantly lower than those in males at 60, 180, and 300 degrees per second. Huston also determined that females had hamstring-to-quadriceps ratios in the 0.40 range.145 Eccentric hamstrings-to-quadriceps ratio was also significantly weaker in female athletes as compared to male athletes.202 It has been hypothesized that hamstring-to-quadriceps ratios lower than 0.60 may predispose an athlete to ACL injury.131
As indicated previously, strength deficits in the female athlete are evident and may play a role in predisposing the female to an ACL injury. If strength may play a role, how does the endurance mode of these muscles play a role in knee stability and injury vulnerability? A study conducted by Rozzi et al247 demonstrated that both males and females had a decrease in the ability to detect joint motion moving into the direction of extension, an increase in the onset time of contraction for the medial hamstring and lateral gastrocnemius muscles in response to landing a jump, and an increase in the electromyogram of the first contraction of the vastus medialis and lateralis muscles while landing a jump when fatigued.234 Research by Zhou et al297 has shown electromechanical delay of the knee extensors to increase by 147% after muscular fatigue. Nyland et al220 looked at the effects of eccentric work-induced hamstring fatigue on sagittal and transverse plane knee and ankle biodynamics and kinetics during a running, crossover cut, or directional change. They determined that hamstring fatigue created decreased dynamic transverse plane knee control demonstrated by increased knee internal rotation during heel strike. Peak ankle plantarflexion moment and decreased knee internal rotation magnitude during the propulsion phase of the cutting maneuver when fatigued is believed to represent a compensatory attempt for knee dynamic stability from the gastrocnemius and soleus.220 Wojtys et al290 also demonstrated the effect of fatigue on knee joint stability. When the quadriceps and hamstrings were exercised to a point of fatigue, there was resultant increase in tibial movement, causing increased vulnerability to ACL injury.290
More recently, combined or partially controllable factors have been suggested as those that have contributions inherent to the individual (intrinsic factors) combined with those that are more extrinsic in nature and, therefore, able to be modified.145 Examples of combined factors are proprioception and neuromuscular control. Both of these factors are affected by an individual’s genetic makeup, but can be taught, to some extent, by structured programs to address their areas of deficiency.119,129,131,132
Proprioception has been defined as the culmination of all neural inputs originating from joints, tendons, muscles, and associated deep-tissue proprioceptors. These inputs into the central nervous system result in the regulation of reflexes and motor control.131 The body receives proprioceptive information by three separate systems. They include the visual system, the vestibular system, and the peripheral mechanoreceptors. When discussing injuries to the ACL, the role of the mechanoreceptors has been the primary focus in the literature. Researchers agree that the ACL does contain mechanoreceptors, but if the central nervous system has a decreased sensory feedback from the knee, there is a decreased ability to stabilize the knee joint dynamically. This places the knee at risk for injury, either microtrauma or macrotrauma.140 Following injury to the capsuloligamentous structures, it is thought that a partial deafferentation of the joint occurs as the mechanoreceptors become disrupted. This partial deafferentation, which is secondary to injury, may be related to either direct or indirect injury. Direct trauma effects would include disruption of the joint capsule or ligaments, whereas posttraumatic joint effusion or hemarthrosis154 can illustrate indirect effects.
Whether a direct or indirect cause, the resultant partial deafferentation alters the afferent information into the central nervous system and, therefore, the resulting reflex pathways to the dynamic stabilizing structures. These pathways are required by both the feed-forward and feedback motor control systems to dynamically stabilize the joint. A disruption in the proprioceptive pathway will result in an alteration of position and kinesthesia.36,262 Barrett38 showed an increase in the threshold to detection of passive motion in a majority of patients with ACL rupture and functional instability. Corrigan,73 who also found diminished proprioception after ACL rupture, confirmed this finding. Diminished proprioceptive sensitivity has also been shown to cause giving way or episodes of instability in the ACL-deficient knee.51 Rozzi et al248 tested proprioception by measuring knee-joint kinesthesia as the threshold to detection of passive motion while moving either the direction of knee flexion or extension. The study determined that females took significantly longer than the males to detect joint motion moving in the direction of knee-joint extension implicating the hamstrings as deficient in proprioception. Injury to the capsuloligamentous structures not only reduces the joint’s mechanical stability but also diminishes the capability of the dynamic neuromuscular restraint system. Therefore, any aberration in joint motion and position sense will impact both the feed-forward and feedback neuromuscular control systems. Without adequate anticipatory muscle activity, the static structures may be exposed to insult unless the reactive muscle activity can be initiated to contribute to dynamic restraint.
The reader is referred to the previous section on gender differences to review the various neuromuscular control factors that vary from female to male. In reference to the female athlete and ACL injuries, the following specific variables will be examined: the muscle firing patterns of the lower extremity with physical tasks, the timing of those muscular responses, and the kinematics and joint position of the lower extremity during activity.
Muscular Activation and Timing Patterns
In a study conducted by Huston and Wojtys,145 different muscular firing patterns were illustrated between females (control and athlete group) and males (control and athlete group). They tested muscular response to anterior translation of the tibia using EMG recordings during a relaxed response to movement and a voluntary muscle contraction response to movement. All 4 groups recruited the gastrocnemius muscle first in the relaxed response to anterior translation of the tibia. The spinal level of muscle firing pattern was gastrocnemius-hamstring-quadriceps for all groups, but as the translation of the tibia continued in the relaxed response phase of the testing, female athletes relied more on quadriceps activity than on hamstrings to stabilize their knee. The predominant muscle recruitment order of the male athletes and both control groups was the hamstring-quadriceps-gastrocnemius muscle pattern. In contrast, the female athletes recruitment pattern was quadriceps-hamstring-gastrocnemius. During the voluntary muscle contraction response, the female athletes demonstrated the same response as the female controls and both male groups. This pattern was hamstring-quadriceps-gastrocnemius. These results support the concept of “quadriceps dominance” in female athletes in terms of muscular recruitment.
With respect to the muscle reaction time in this study, no significant differences were found at the spinal cord level for the quadriceps and hamstrings; however, the male and female athletes produced significantly faster gastrocnemius muscle responses compared to the two control groups. In the intermediate phase of the relaxed response testing and the voluntary response to tibial translation, there was no significant difference for all muscles between all 4 groups. When testing muscular strength and time to reach this peak force utilizing isokinetic testing, Huston and Wojyts145 found no differences in time-to-peak torque for knee extension at 60 and 240 degrees per second for all groups. Significant differences did exist between male and female athletes for hamstring time-to-peak torque at 60 and 240 degrees per second. The female athletes were statistically significantly slower than the male athletes and minimally slower than the female control group, although this difference was not statistically significant.145 Contrary to Huston and Wojyts, Rozzi et al248 did not find sex differences in the time-to-peak torque tested isokinetically for either hamstrings or quadriceps. This same study did find significantly greater EMG peak amplitude of the lateral hamstrings for the female athletes when landing from a jump on 1 leg. The authors stated that this finding may be related to the idea that female athletes possess inherent joint laxity and the hamstrings must activate at a higher level to provide stability to the joint.248
The latency period between sensory feedback and dynamic movement is known as electromechanical delay and has been shown to be shorter in males compared to females, thus allowing superior efficiency of dynamic stabilization in males.170
DeMont et al86 studied the muscular activity before foot strike in various functional activities for ACL-deficient subjects, ACL-reconstructed subjects, and a control group, and compared involved to uninvolved legs of each subject. All subjects were female. The tasks consisted of downhill walking, running, hopping, and landing from a step. Different bilateral activation of vastus medialis obliques occurred with downhill walking and running activities for the ACL-deficient group. The ACL-deficient group also showed a significant increase in vastus lateralis activation during running and landing when compared bilaterally and also when compared to ACL reconstructed and control group subjects. Activation of the lateral gastrocnemius was lower in downhill walking and higher in the landing task in the ACL-deficient group also. The ACL-reconstructed group showed significant differences between the involved and uninvolved limb in the lateral gastrocnemius for the hop. These side-to-side differences for the ACL-deficient and ACL-reconstructed groups, and group differences between ACL-deficient and control groups, suggest that the females with an ACL-deficient knee use unique strategies involving the vastus medialis obliques, vastus lateralis, and lateral gastrocnemius, and these muscles need to be addressed in the rehabilitation process. A similar study performed by Swanik et al274 demonstrated ACL-deficient subjects to exhibit greater peak activity (as measured by isometric electromyography) in the medial hamstring in comparison with the ACL-reconstructed group and greater peak activity in the lateral hamstring than the control group during running. During landing from a step, the ACL-deficient group demonstrated significantly less isometric EMG activity in the vastus lateralis when compared to the control group. These findings suggest the importance of the hamstrings in controlling anterior tibial translation and rotation, as well as their possible role in inhibition of the quadriceps in an effort to dynamically stabilize the knee in the ACL-deficient knee.
For dynamic stabilization to occur at the knee, many muscles are involved that directly pass around the joint as well as other muscles that are distally and proximally positioned but play a role in controlling the forces at the knee. Baratta et al34 investigated muscular coactivation patterns at the knee. Subjects consisted of nonathletes, recreational athletes, and highly competitive athletes, and EMG data were collected during an isokinetic strength test. High-performance athletes with hypertrophied quadriceps had inhibitory effects on the coactivation of the hamstrings compared to the recreational athletes. They also determined that athletes who routinely exercised their hamstrings demonstrated inhibited quadriceps and had coactivation patterns similar to those of the nonathletes. Muscular balance is key to efficient dynamic joint stabilization.
Muscle stiffness is important to stability of the knee and demonstrated when muscles surrounding the knee contract, offering the joint increased contact force and decreased joint mobility. Markolf et al186 reported that nonathletes could increase varus and valgus knee stiffness 2 to 4 times with isometric contraction of the hamstrings and quadriceps. Athletes in the same study were able to increase their joint stiffness by a factor of 10 with the same isometric contraction. Bryant and Cooke56 demonstrated gender differences in knee stiffness in a study in 1988. When testing varus and valgus stiffness, females rotated at the tibia 66% more than the males and were 35% less stiff. Another study that looked at gender differences in the anterior-posterior plane of motion determined a significant difference in females, and males, ability to stiffen the knee joint. Men were able to increase their joint stiffness by 4 times, whereas the females were only able to stiffen their joint by 2 times.146 The exact mechanism of knee stiffness is not completely understood, although a study by Such et al determined that lower-extremity muscle mass had the largest influence on the stiffness properties of the knee.273
Knee Kinematics and Landing Characteristics
As noted in the previous section on the mechanisms of injury, it is well documented in the literature that most of the ACL injuries occur when landing from a jump or during deceleration and pivoting. It has been documented that the quadriceps exerts its maximum anterior sheer force when the knee flexion angles are the smallest (20 to 25 degrees flexion), which places a measurable strain on the ACL.260 Eccentric activation of the quadriceps at high velocities present during athletic movements may produce too much force for the static and dynamic stabilizers of the knee to resist, thus allowing injury to occur. EMG studies demonstrate eccentric quadriceps muscle activation during such activities as running, cutting, and landing from a jump to be more than 2 times greater than maximum voluntary contraction.119 It has also been documented in the literature that there is a significant difference in how males and females perform the previously noted movement patterns.
Malinzak et al179 were one of the first research groups to investigate these kinematic gender differences. EMG and 3-dimensional kinematic analyses of cutting and running were obtained from male and female athletes. Females demonstrated significantly less knee flexion, increased knee valgus, and decreased hip flexion than males during both of these movement patterns. Females also had greater quadriceps and lower hamstring activation levels especially at heel strike.144 Colby et al72 investigated 4 different cutting maneuvers in males and females using 2-dimensional video analyses and electromyography and had similar results as Malinzak et al.179 The average knee flexion angle was 22 degrees for each cutting maneuver. Quadriceps activity was 161% of the maximum voluntary isometric contraction as compared to 14% of the maximum voluntary isometric contraction for hamstring activity.72 This further demonstrates the “quadriceps/-dominant” state and how weak hamstrings or hamstring/quadriceps muscular imbalances present in female athletes could contribute to their susceptibility for ACL injuries.
Lephart et al170 also investigated strength and lower-extremity kinematics during landing. Single-leg landing and forward hop tasks were studied using electromyography and force plates with female basketball, volleyball, and soccer players, and matched male subjects. This study also tested strength of the quadriceps and hamstrings via isokinetic testing. The following results were all significant at the level of p < 0.05. For single-leg landing, females had greater hip internal rotation, less knee flexion, and less lower-leg internal rotation. The females also had significantly less time to maximum angular displacement of knee flexion. During the forward hop task, females had less knee flexion, less lower-leg internal rotation, and more time to maximum angular displacement for hip internal rotation and less time to maximum angular displacement for knee flexion. There were no significant difference for vertical ground reaction force variable for both landing and hopping tasks. Isokinetic testing revealed significant lower peak torque to body weight for knee extension and flexion (p < 0.05). Overall, the females landed in a more valgus position and with less knee flexion, thus less time for absorption of the impact forces. The weakness demonstrated in the quadriceps and hamstrings may also play a role in the landing kinematics.170
In a follow-up study to Malinzak, Chappel et al64 hypothesized that female recreational athletes would have increased proximal anterior tibial shear force, knee extension moment, and knee valgus moment while performing forward, backward, and vertical stop-jumps. The results of this study are similar to those of previous studies. Women exhibited greater proximal tibia anterior shear force than did men during the landing phase of all jumps. All subjects exhibited greater proximal tibia anterior shear force during the landing phase of the backward stop-jump task than during the other 2 stop-jumps. Women also exhibited greater valgus and extensor moments than did the males for all 3 stop-jumps.
Ground reaction force differences during landing are an interesting kinematic variable to examine between males and females. Dufek and Bates94 examined landing forces and pointed out that higher landing forces had a positive relationship with injury occurrence. Hewett et al132 examined the results of a neuromuscular training program and determined that the training program resulted in significant decreases in peak landing forces and decreases in valgus-varus moments at the knee. They indicated that the valgus-varus moments at the knee served as significant predictors of peak landing forces. This same study demonstrated that the males’ landing forces were an average of 2 bodyweights greater than the females, yet they have lower rate of serious injury. It has been hypothesized that high landing forces by the males are dissipated through increased knee flexor activity at the instant of landing and greater angular knee flexion at landing. Both of these strategies may allow males to dissipate ground reaction forces more efficiently.
The previously mentioned studies have all looked intimately at the knee joint. But what effects do the trunk, hip, and ankle have on the kinematics of the knee joint? Bobbert and van Zandwijk48 described, in their research, the knee being “slaved” to the moment produced at the hip. It has been theorized that, because most females have weak hip extensors, they use the iliopsoas for trunk control over their hips and land in a more erect posture and have greater extensor moments at the knee. Decreased trunk flexion also decreases maximal quadriceps and hamstrings activation, thus decreasing dynamic stabilization directly at the knee joint. Observation of videotapes of ACL injuries has demonstrated that two-thirds of the injuries occurred when the center of gravity appeared behind the knee. Another theory regarding this variable is that during upright landings, the rectus femoris may act as a hip stabilizer and pull the trunk forward. This powerful contraction by the rectus femoris may also produce a large tibia anterior shear force. More research needs to be performed to prove or disprove these theories, but trunk and hip control appear essential to efficient athlete maneuvers and should be part of all prevention and rehabilitation programs.
In summary of the extrinsic and combined factors that may predispose the female athlete for higher incidence of ACL injuries, the following items were revealed:
Females are weaker in their quadriceps and hamstrings as compared to males.
Females have a lower hamstring-to-quadriceps ratio as compared to males.
When both men and women are fatigued, the stability of the knee joint is compromised.
ACL-deficient subjects have decreased proprioception.
Females are slower to detect proprioception as measured by detection of passive movement in the direction of knee extension as compared to males.
Females use more of a quadriceps-hamstring-gastrocnemius muscle firing pattern in response to anterior tibia translation and males use more hamstring-quadriceps-gastrocnemius pattern.
Females are slower to reach peak torque for the hamstring group as compared to males.
Females have a longer electromechanical delay between stimulus and action as compared to males.
Females demonstrate a decrease in muscle stiffness and thus decreased ability to stabilize knee joint as compared to males.
Females demonstrate the following patterns when landing from a jump or decelerating
Decrease in knee flexion
Increase in knee valgus (see Figure 31-3)
Increase in hip internal rotation (see Figure 31-3)
Decrease in trunk and hip flexion
As noted previously, many research studies have focused on determining the exact cause of the higher frequency of ACL injuries in females as compared to males. Although much time has been spent on this subject, no definitive intrinsic, extrinsic, or combined factors have been identified as strong predictors of ACL injuries. A study by Arendt et al,25 published in 1999, set out to determine potential patterns that cause ACL injuries by using the NCAA Injury Surveillance System. The conclusions of this study stated that common noncontact ACL injuries mechanism were pivoting or landing from a jump. They found no comorbidity or illness patterns. The injured athletes were experienced, with many years of sports participation before and during high school. Hyperextension was the only physical examination feature that could possibly be linked to ACL injuries. Females were more likely to be injured just prior to or just after their menses and not midcycle.25 Because of the multifactorial presentation of this injury, the sample size for such a study must be quite large to be predictive. These authors stated that their project was to be viewed as a pilot study and hoped it would stimulate more research in this area. Subsequently, many researchers have attempted to formulate skill-related tasks and functional assessments that could accurately predict the risk of ACL injury.
Based on this information, should the clinician working with these athletes conduct a screening process in an attempt to identify those athletes at risk and thereby institute prevention programs to minimize the incidence of ACL injuries among their athletic teams? Current research and practical knowledge do not offer a single valid and reliable screening tool, although some evidence exists that a examining a set of variables (body mass, tibial length, knee valgus, knee flexion during landing, and hamstring-to-quadriceps ratio) may assist in the prediction of athletes prone to high loads during landing.206 Most clinicians do not have access to the technology and equipment necessary to examine balance, proprioception, kinesthesia, neuromuscular patterns, or kinematic analysis of forces and angles. This does not mean the clinician cannot look at the athlete with simple functional testing. Strength and muscular endurance can be examined either isokinetically or with one repetition maximum testing. Functional tests, such as single-leg and tandem stance balancing, can screen for basic proprioception deficits, and single-leg hop tests, vertical jump, and the tuck jump assessment can assist in grossly examining explosive power of the lower extremity and dynamic stability at the hips and knees. Observing joint positions and landing characteristics from a jump, both visually and with simple video analysis, is an easy thing for the clinician to do. Incorrect technique or motor performance deficits that can be identified can then be corrected to enhance physical performance and possibly lower injury risk, especially for the female athlete.
Injury prevention programs have been developed and tested based on the previous information with the goal of enhancing physical performance and decreasing injury occurrence among female athletes. The authors of this chapter believe that addressing the previously stated deficits common to female athletes can only enhance their physical performance and as a result may decrease the risk of ACL injury. Both high-tech screening and low-tech (clinical) screening procedures are important. When a deficit is identified, it should be addressed, and only good things can come from any education or improvement that occurs.
Prevention and Exercise Considerations
As noted previously, the research indicates some possible areas where females and males differ in their muscle physiology, biomechanics, hormonal levels, joint stability, joint kinematics, proprioception, and skill level in athletics. Which of these factors are controllable and what has the research determined as the best approach for injury prevention? That is the question we all ask ourselves. Although this topic of injury prevention for ACLs has received much attention lately, it is not a new topic. Henning was investigating this idea in the early 1980s, and after a 10-year study of ACL injuries in female basketball players, he formulated a prevention program based on altering the “quad-cruciate interaction.”119 As previously mentioned, Henning concluded that the most common mechanisms of injury to the ACL were planting and cutting, straight-leg landing, and 1-step stop with the knee hyperextended.119 His prevention program consisted of activities to eliminate or minimize these mechanisms. Henning proposed using an accelerated rounded turn off a bent knee instead of the pivot-and-cut movement pattern. He also emphasized drills that worked on landing on a bent knee and a 3-step stop with the knee bent. The common thread in all the drills was the bent knee position. It has also been illustrated in research studies discussed in the previous sections of this chapter that females do land from jumps with a straight-leg position and have excessive valgus knee position with landing and cutting movements during sports (see Figures 31-3 and 31-7B). Both of these positions put the females at risk for an ACL injury. Henning’s prevention program did show some success in decreasing ACL injuries (89% decrease). Although his program did have its limitations, it was an admirable start in addressing this problem and provided impetus for modern prevention programs.
Proprioception deficits in ACL-injured and ACL-reconstructed patients is well documented. So, it only seems natural to look at this component and incorporate it into a prevention program. Caraffa et al60 did just this in developing their 5-phase proprioceptive program that progressed the athlete through increasingly difficult skills using different balance boards. The study showed a statistically significant decrease in ACL injuries in semiprofessional and amateur soccer players for the exercise program versus the control group of skill-matched soccer players. The study received criticism for not being randomized and for flaws in program standardization, but it can be looked at as a pilot study and a plausible approach to developing a prevention program incorporating proprioception training.
In the mid-1990s, Hewett et al132 conducted a seminal study to determine the effect of jump training on landing mechanics and lower-extremity strength in 11 female athletes involved in jumping sports. Vertical jump height, isokinetic muscle strength, and force analysis testing were performed prior to and after the training program for the female athletes and a group of male athletes. The jump program was performed over a 6-week period and was performed on alternate days, 3 days a week. During the jumping program, 4 basic techniques were emphasized:
Correct posture with spine erect, shoulders back, and body alignment of shoulders over knees throughout the jump. Control of the trunk over the body is important.
Jumping straight up with no excessive side-to-side or forward-backward movement.
Soft landings, including toe-to-heel rocking and bent knees.
Instant muscular recoil for preparation for the next jump.
See Appendix A for details of the Jump-Training Program.132
The results of the training program for the female group revealed peak landing forces decreased 22%, knee varus-valgus moments decreased approximately 50%, and hamstring-to-quadriceps peak torque ratios increased 26% on the nondominant side and 13% on the dominant side. Hamstring power increased by 44% with training on the dominant side and 21% on the nondominant side. Mean vertical jump height also increased by 10%. Multiple regression analysis revealed that varus-valgus moments were significant predictors of peak landing forces.132
The results of this study led the researchers to continue with a follow-up project with this jump-training program. Hewett et al129 developed a prospective research study to determine the effect of this same jump-training program on the incidence of knee injury in female athletes. They monitored 2 groups of female athletes; 1 group performed the jump-training program and 1 group did not. A group of untrained male athletes were also used for comparison. The groups were monitored throughout the high school soccer, volleyball, and basketball seasons. Results of this study revealed that the untrained female athletes had a 3.6 times higher incidence of knee injury than trained female athletes (p < 0.05) and 4.8 times higher incidence than male athletes (p < 0.03). The incidence of knee injury in trained female athletes was not significantly different from that in the untrained male athletes.129 The results of this early, innovative study indicated that a plyometric training program may have a positive effect in reducing incidence of female ACL injuries. The authors of this study acknowledged several limitations to their study. It was not a randomized, double-blind study, and there were not equal numbers of each type of sports participant in each group. Conclusions from this study indicate that the plyometric training program decreased the magnitude of varus-valgus moments at the knee and improvement in hamstring-to-quadriceps strength ratio. As noted previously, many researchers believe that these 2 lower-extremity variables, as well as trunk motion, play a strong role in ACL injury in female athletes.106,132,216 However, it should be noted that the results from contemporary research suggest that a prevention program must train roughly 89 female athletes in order to prevent 1 ACL injury when applied generally to a group.206
An interesting fact to note about many of these prevention programs is the component of educating the athlete about how to correctly perform landing or cutting tasks. Henning developed a teaching tape consisting of examples of noncontact ACL injuries followed by illustrations of the recommended drills done in the gym as well as on the playing field. He stated that young athletes are more receptive to technique modification and called it “improved player technique skills.”119 Ettlinger et al101 stated that ACL injuries in alpine skiers could be reduced as much as 60% by using standardized training programs before the ski season. The subjects were trained to avoid high-risk behavior, recognize potentially dangerous situations, and to respond quickly whenever these conditions were encountered. Hewett et al132 used verbal cueing to encourage proper jumping and landing techniques. Such phrases as “on your toes,” “straight as an arrow,” “light as a feather,” “shock absorber,” and “recoil like a spring” were all used to illustrate proper technique. Similarly, Myer et al used the tuck jump assessment task and both verbal and visual feedback during the task to fine-tune and attempt to correct jumping and landing strategies.205 The authors of this chapter also use 3 words beginning with the letter L to instruct athletes in correct performance of all motor skills: Low, Light, and (in) Line. These cues refer to low, flexed knee landings and transitions; softness and quietness during landings; and parallel thighs during activity, respectively. This pneumonic is also referred to as L3.
Another important study by Onate et al224 reported the importance of feedback and educating the athletes in proper technique performance. They looked at the effects of augmented feedback versus sensory feedback on the reduction of jump-landing forces. The augmented feedback group received information on how to land softer via video and verbal analysis, the sensory feedback group was asked to use the experience with their baseline jumps to land softer, and the control groups were given no extraneous feedback on how to land softer. The subjects in the augmented feedback had significantly reduced peak vertical ground reaction force as compared to the sensory feedback and control groups.224 All clinicians and researchers must remember that even though you may have the perfect prevention program, if your subjects do not understand the movement pattern and technique you are asking them to perform, it is all for naught.
Myer et al204 examined a comprehensive neuromuscular training program to study the effects on lower-extremity biomechanics and improved performance in the female athlete’s vertical jump, single-leg hop, speed, bench press, and squat. As previously discussed, multiple research studies have been carried out examining the positive effects of a plyometric or jump-training program; however, this study combined plyometrics with core strengthening, balance training, interval speed training, and resistance training.204 Fifty-three female athletes involved in basketball, volleyball, or soccer participated. Forty-one subjects were assigned to the training group and 12 to the control group. Pretesting was conducted 1 week before the training program and posttesting 4 days after the final training session. The athletes received feedback on biomechanical analysis and correct technique before and after training sessions. The 90-minute training sessions were held 3 days a week (Tuesday, Thursday, and Saturday). Table 31-3 provides a breakdown of the training sessions. Subjects trained for 6 weeks, while control subjects did not change their normal exercise program. Results demonstrated statistically significant improvements compared to their pretrained values in vertical jump height, single-leg hop distance, sprint speed, bench press maximum, and squat maximum for the trained group. Knee flexion range of motion (ROM) during landing from a box jump was significantly increased. Varus and valgus torques were significantly lower for the right knee and showed a trend toward decrease valgus torque in the left knee. The control group showed no increase in any of the previously measured parameters over a 6-week period.204 This study supports the benefits of a comprehensive exercise approach when treating the female athlete. A combination of plyometrics, core strengthening, balance training, upper- and lower-body strengthening, speed training, and, very importantly, education on technique proves to be valuable in improving athletic performance, as well as in decreasing potentially dangerous variables in knee biomechanics when running and jumping.106
Table 31-3Neuromuscular Training Program Schedule ||Download (.pdf) Table 31-3 Neuromuscular Training Program Schedule
|Tuesday ||Thursday ||Saturday |
30-minute plyometric station
30-minute strength station
30-minute core-strengthening and balance station
| || |
Mandelbaum et al182 performed a recent prospective study similar to the previous studies to examine prevention of ACL tears in the female athlete. The authors developed a community-based program named the “Prevent Injury and Enhance Performance Program,” which was created specifically for female soccer players between the ages of 14 and 18 years. This program consists of basic warm-up activities, stretching techniques for the trunk and lower extremities, strengthening exercises, plyometric activities, and soccer-specific agility drills. The program also places heavy emphasis on proper landing technique. This training program was implemented to address the feed-forward mechanism as described previously. The specific goal was to improve the athlete’s ability to anticipate external forces or loads to stabilize the knee joint, protecting the inherent structures.182
Results of this study using the “Prevent Injury and Enhance Performance Program” were impressive in reducing ACL injury in soccer players. Analysis of data from the first year of the study revealed an 88% overall reduction in ACL injury compared to the control group followed by a 74% reduction of ACL injury during the second year of the study. The authors concluded that prophylactic training focusing on developing neuromuscular control of the lower extremity through strengthening exercises, plyometrics, and sports-specific agilities drills “may address the proprioceptive and biomechanical deficits that are demonstrated in the high-risk female athletic population.”182, p. 1008 These researchers and others continue to study the “Prevent Injury and Enhance Performance Program” with a variety of populations.
When designing an exercise program for any athlete, and especially the female athlete, the authors of this chapter like to use the lower-extremity reactive neuromuscular training sequence described in Table 31-4. The basic premise of the exercise sequence is to begin with a stable base of support in a closed-chain position. Then, progress with resistance and perturbations from resistance or trunk and upper-extremity movements. When the athlete becomes proficient with the exercises performed with a stable base, the base is then narrowed and an environment of instability is created.
Table 31-4Lower-Extremity Reactive Neuromuscular Training, From Less to More Difficult (Top—Less Difficult, Bottom—Most Difficult) ||Download (.pdf) Table 31-4 Lower-Extremity Reactive Neuromuscular Training, From Less to More Difficult (Top—Less Difficult, Bottom—Most Difficult)
|Description of Activity ||Examples ||Figure Demonstratinga |
|Stable base, bilateral lower extremities ||Partial squats, step down and hold ||None |
|Unstable base, bilateral lower extremities ||Wobble boards, foam rollers ||None |
|Stable base, unilateral lower extremity ||Single-limb stance, unilateral squats star diagram, contralateral LE tubing (“steamboats”) ||Figures 31-5 and 31-6A and B |
|Unstable base, unilateral lower extremity ||Wobble boards, foam rollers, minitramp ||Figure 31-7A and B |
|Stable base, with added UE/trunk challenges ||Squat positions with ball throws, perturbations ||None |
|Unstable base, with added UE/trunk challenges ||Wobble boards, foam rollers, DynaDiscs, with ball throws, perturbations ||Figures 31-8 and 31-9 |
|Jump/landing sequence from stable base ||Jump/land on gym floor, Jump/land from minimal elevation (stair, mat) ||None |
|Jump/landing sequence from unstable base ||Jump/land from mini-tramp ||Figure 31-10A and B |
|Jump/landing sequence with distractions ||Jump/land with twists, external resistance, passing balls ||None |
The progression repeats with an unstable base of support. Sport-specific training is added next with the goal of neuromuscular control becoming a natural, noncognitive, adaptation to the movement patterns required by the sport. The following are some ideas we have developed based on our clinical experience, as well as being creative with the exercise progression.
Based on the previous descriptive information about female neuromuscular and functional strategies, how does the rehabilitation professional gets the females to bend their knees, avoid the valgus knee position, and get their gluteal region down with the trunk flexed to minimize the potential risk of knee injury? We propose that you make the athlete’s exercise program focus on these exact positions (see Figure 31-11).
Strengthening the quadriceps and hamstrings in the flexed trunk and knee position can be performed with simple wall sits, step-down position with a static hold (see Figures 31-4 and 31-5) and progress into closed-chain squats in a protected position using the Smith Squat Rack. The key part of this squat is to note that the athlete never fully extends knee and works in a range of 30 to 90 degrees of knee flexion and uses the bench as her spotter. This is the position we want her to assume when performing sports, so we must train her muscles in this position. What about powerlifting techniques for females, such as the power clean or snatch? The purpose of these powerlifting movements should not be for brute strength but rather for quick footwork and bent knee position with trunk stabilization. Female athletes often do not do the simple squat technique performed by most males in all levels of sports. Proper technique for free-weight lifting is the key, and lighter-weight body bars are optimal for learning, rather than the heavy 45-lb standard weightlifting bars. The Smith squat machine is also useful for early control of the bar during squats and other upper extremity lifts. Treadmill retro uphill walking in a knee-flexed position is also effective for working the quadriceps in an optimal position. If the hamstrings are to be active when the trunk is flexed, then they also need to be strengthened in a flexed trunk position such as seated open-chain resisted knee flexion. Another way to work the gluteals and hamstrings in a closed-chain trunk flexed position is to do a semisquat uphill walking lunge on a treadmill. This is the reversal of the retro uphill squat walk.
Example of a unilateral stable base exercise
Note the incorrect valgus and internal rotation. Training must be done with the lower extremity in proper alignment.
Better stance lower-extremity position
Subjects must be corrected and coached to work in excellent lower-extremity alignment. Note that this can also be done in mirror for visual feedback and corrections.
Single limb stance hip abduction/adduction with elastic resistance to offer perturbation. AKA “Steamboats” (A) Start position (B) Finish position.
A. Unstable surface (1Ž2 foam roll) balance activity. B. Same activity with use of mirror for visual feedback on lower extremity positioning during the task.
Subject, on DynaDisc/unstable base on DynaDisc (unstable base, 1 lower extremity) throwing a ball to/from another person for distraction/balance perturbation.
Unstable base, unilateral lower extremity exercise, with distraction/perturbation technique of ball throw/catch.
Dynamic jump/land training
Subject shown airborne after jumping off minitramp (A). Subject landing from jump (B). During exercise training, stress correct lower extremity position and “soft landing.”
Single limb plantar flexion, training the plantar flexors in the “down low” position.
Another possibility is to combine strengthening and neuromuscular retraining. In Figure 31-12, the athlete is performing a unilateral, closed-kinetic chain partial squat on the Total Gym, using a DynaDisc under her foot, thereby performing both types of exercise concurrently. This is an example of an unstable base used during a unilateral strengthening activity.
Use of DynaDisc on Total Gym for strength training
Single-leg partial squats with an unstable surface. Close attention is paid to the position and alignment of the lower extremity. Foot position shown could be improved.
Muscular fatigue slows electromechanical delay, decreases knee stability, and compromises proprioception.220,247 Muscular fatigue will happen to all athletes if they compete at an intense level, so the athlete must be trained to have a stable knee even when fatigued. Fatiguing the athlete and then carefully working on proprioception, cutting and deceleration maneuvers, and proper landing position from a jump are possible techniques for training, although controversial.
When the big picture of total-body positioning is examined, attention must be paid to the joints distal and proximal to the knee joint. Often the ankle and its role as the first link of the chain to absorb the forces and then stabilize the base of support are forgotten. Adequate motion of the talocrural and the subtalar joints must be present for normal landings to occur. The gastrocnemius and soleus have a role in posterior stabilization of the knee joint and need to be strengthened in the position in which they must excel: knee and trunk flexion (see Figure 31-11). In the study by Huston and Wojtys,145 the gastrocnemius was the first muscle to respond to tibia anterior translation in the relaxed position. An intriguing thought is that maybe the foot and calf muscles are the key to knee stability, as they are the first line of defense for all closed-chain activities. The trunk and hips are the joints proximal to the knee, and they possess the most muscular mass and thus the most potential for efficient body control. We call this concept “The Butt and Gut” and believe firmly in its role in proficient movement patterns for all joints of the body. Females are usually weaker in their gluteal muscles and lack some trunk control with high-level sports movements. Emphasis on hip rotators, hip extensors, transverse abdominals, and hip adductors strength and endurance should be part of every athlete’s fitness program. With strong hip and trunk muscles, the landing and running characteristics of genu valgus, hip internal rotation, straight knee position at foot impact, and erect trunk position should be minimized and possibly eliminated.105,130,133
Educating your athletes in proper movement patterns is the key to success for injury prevention. As noted previously, research shows that visual and verbal cueing enhances the performance of proper technique in the quest for optimal position of the body for injury prevention and efficient, powerful sports movements. Simple video can be used to record an athlete during a movement or task, allow the athlete to see what they look like performing the task, and identify what improvements could be made and what the goal is regarding proper technique.
Excellent clinicians frequently review the literature and then think of bold, creative ways to exercise their patients based on the positions that make the female athlete vulnerable to ACL injury. Although ACL reconstructive surgery provides excellent, predictable outcomes in most cases, and rehabilitation after ACL reconstruction has become standard physical therapy practice, no reconstructed knee is as good as an uninjured knee. In the world of ACL injuries in female athletes, the mother’s old quote “an ounce of prevention is worth a pound of cure” rings true.
Sequelae from Anterior Cruciate Ligament Injury
We refer the reader to Chapter 24 for a complete analysis of the information regarding evaluation and treatment of the female athlete (or any athlete) suffering an ACL injury. Prevention of this debilitating injury cannot be more emphasized with the growing concerns that have been raised among the sports medicine community regarding the early degenerative changes after a knee injury and specifically following an ACL injury.81,82,98,114,244,246 Curl et al reviewed more than 30,000 knee arthroscopies with a variety of patient ages and reported chondral injuries in 63% of these patients, with an average of 2.7 articular cartilage injuries per knee.79 Bone bruises, most common in the lateral compartment, are observed in 80% of MRI studies following ACL tear.198 At the time of surgery, 9% of all ACL injured patients have documented acute cartilage defects. This same population demonstrates a 19% incidence of articular cartilage defects at 9-year follow-up.246 This significant increase in cartilage defects demonstrates that stabilization of the knee through ACL reconstruction does not eliminate the risk of degenerative changes in the articular cartilage.13,14 In fact, many current studies indicate that despite reconstruction of the injured ACL, patients will develop osteoarthritis within 5 years after surgery. In a systematic review conducted by Oiestad et al, the authors reported that up to 13% of those with isolated ACL injuries and 24% to 48% of those with ACL plus other concomitant knee injuries experienced demonstrable osteoarthritis within 10 years, lower than some of the reports in the literature.223 Whether this is a result of subclinical or unrecognized osteochondral or meniscal injury concomitant with the ACL injury or the reconstructive surgery is unknown.
Numerous studies show good-to-excellent results following ACL reconstructive surgery with reference to stability, normal knee mobility, normalized strength, and return to previous level of activity.10,28,81,82,143,153,185,221,258,266 Work completed by Daniels et al was the first to document concern regarding early degenerative changes in knees that had stability restored with an ACL reconstruction in 5-year80 and 10-year follow-up studies.81 At 5- to 20-year follow-up, patients post-ACL reconstruction demonstrate up to a 50% increase in radiographic changes associated with arthritis compared to the contralateral, uninjured knee.229 Concern regarding such degenerative changes was expressed by Gilquist who wrote that these surgeries resulted in “giving the patient enough security to go back to strenuous sports and then [ruin] the knee.”114 This concern is valid, but one must consider the concept of joint function and define “full” function.
Dye describes the knee joint as a mechanical engineering model with a complex, metabolically active system for transmission of forces among the femur, tibia, fibula, and patella, with cruciate ligaments acting as linkages, articular cartilage and menisci as weightbearing entities and force absorbers, and muscles as force generators and absorbers.98 In our view, the concept of musculoskeletal function includes the capacity not only to generate, transmit, absorb and dissipate loads but also to maintain tissue homeostasis while doing so.97
This statement beautifully illustrates our belief that joint function is not truly attained unless the system can escape from tissue destruction or degeneration while completing a desired level of functional activity. Dye presents the concept of “envelope of function,”96 which is the safe zone of loading that a system can maintain normal homeostasis as illustrated in a load distribution curve (see Figure 31-13). Below this safe zone is the subphysiologic loading zone, causing loss of tissue homeostasis secondary to decreased loading, which results in such injuries as osteopenia and muscular atrophy. Above the “envelope of function” is a zone of structural failure with loads great or frequent enough to cause actual failure of an element of the system, such as a meniscal or ACL tear. The zone that is immediately above the envelope of function, the zone of supraphysiologic load, represents loads at a force or frequency that cause a disruption of the tissue homeostasis before failure, that is, stress fractures or articular cartilage degeneration.
Anatomic cylinder of trunk
The muscle contraction of “drawing in” of the abdominal wall with an isometric contraction of the lumbar multifidus. The interrelationship and the interaction between these 2 muscles and the fascial system can be appreciated, and the figure illustrates how they can work together to give spinal support. (Reproduced, with permission, from Richardson C, Jull G, Hodges P, Hides J. Therapeutic Exercise for Spinal Segmental Stabilization in Low Back Pain: Scientific Basis and Clinical Approach. Edinburgh, UK: Churchill Livingstone; 1999.)
This concept of “envelope of function” correlates nicely with the Wolff law that states cyclical loading of the cartilage and bone results in increased strength and durability of these structures and ultimately the musculoskeletal system. However, excessive loading results in degradation of the cartilage microstructure and arthritic changes.181 Maintaining activity within the “envelope of function” results in maintenance of tissue homeostasis and the ability to strengthen the musculoskeletal system, while exceeding this physiologic loading and moving into the “supraphysiologic loading zone” with increased intensity, duration, or frequency of activity results in degradation of the system and disruption of tissue homeostasis. Sports medicine personnel involved in the orthopedic medical care of a female athlete should adhere to the principle of remaining in the zone of homeostasis as defined by the current status of the joint involved. Defining this zone is a difficult task after completing the rehabilitation following an orthopedic injury such as an ACL tear and surgical reconstruction. The challenge of attaining a level of activity (loading) of the injured joint to allow tissue building, such as muscular hypertrophy, without entrance into the zone of supraphysiologic loading (overloading) that could affect articular cartilage degeneration or meniscal irritation, requires extreme care in planning with respect to activity intensity, duration, and frequency. Determining such a zone also requires excellent communication between the surgeon and the rehabilitation professional regarding any preexisting conditions and surgical findings. Astute observation of the sports medicine specialist for signs of inflammation with a prescribed rehabilitation program and allowed functional/sporting activities is necessary to ensure proper physiologic loading.
The physically active female may be at greater risk than her male counterparts for articular cartilage degeneration and concerns. Gender difference in the knee joint size and greater valgus alignment may result in a greater stress concentration in the lateral and patellofemoral compartments of the female’s knee. MRI studies of the human knee demonstrate that females have significantly less cartilage thickness and volume than age-matched males.68 Articular cartilage has a complicated organization of hyaline cartilage with an extracellular matrix composed principally of type II collagen and sparsely distributed chondrocytes. Animal studies also document lower levels of proteoglycan and collagen in the cartilage of female rats. Considering the increased incidence of ACL injury in females versus males and the female articular cartilage basic science, chondral injury concerns are well founded.
Core Stabilization for the Female Athlete
The common prerequisite for participation and success in all types of sports is a strong and stable core of the human body. Control of balance in upright posture and stability of the segments of the spine are required not only for activities of daily living but also for high-level sports activity.100 This stability enables athletes to transmit forces from the earth through the kinetic chain of the body and ultimately propel the body or an object using the limbs.74 The concept of core stabilization of the trunk and pelvis as a prerequisite for movements of the extremities was described biomechanically in 1991.52 Subsequently, core stabilization has become a major trend, both in treatment of injuries and in training regimes used to enhance athletic performance and prevent injury.
Many terms and rehabilitation programs are associated with the concept of core stability, including lumbar stabilization, dynamic stabilization, motor control (neuromuscular) training, neutral spine control, muscular fusion, and trunk stabilization.12 The core has been conceptually described as either a box or a cylinder241 because of its anatomical and structural composition. The abdominals create the anterior and lateral walls; the paraspinals and gluteals form the posterior wall, while the diaphragm and pelvic floor create the top and bottom of the cylinder, respectively (Figure 31-14). Additionally, hip girdle musculature reinforces and supports the bottom of the cylinder. Envisioning this cylindrical system helps to understand its function as that of a dynamic muscular support system, described by some authors as the powerhouse, engine, or a “muscular corset that works as a unit to stabilize the body and spine, with and without limb movement.”12, p. S86
Proximal stability for distal mobility is a commonly understood principle of human movement. It was originally described by Knott and Voss159 and applied in the concepts associated with proprioceptive neuromuscular facilitation. Nowhere is the concept of dynamic proximal stability more important than in sports. Without proximal control of the core, athletes could not use the lower extremities to propel the body in running and jumping or use the upper extremities to support or propel the body (in activities such as gymnastics and swimming), or to manipulate, use, and throw objects (such as throwing a shot put or softball, or using a tennis racquet). The core is in the middle of the human kinetic chain and serves a link between the upper and lower extremities. This allows for transfer of energy from the lower to the upper extremities and vice versa.
Strength and coordination of the core musculature is vital to performance and generation of power in many sports. When the core is functioning optimally, muscles elsewhere in the kinetic chain also function optimally allowing the athlete to produce strong, functional movements of the extremities (Table 31-5).65,156 Even small alterations in the kinetic chain have serious repercussions throughout other portions of the kinetic chain and thus on skills that are based upon efficient utilization of the entire chain.156 Therefore, without proper stabilization and dynamic concentric and eccentric control of the trunk during athletic tasks, the extremities or “transition zones” between the core and extremities can be overstressed (ie, hip and rotator cuff).
Table 31-5Examples of Core Demands, Kinetic Chain Relationships, and Outcomes of Specific Sporting Tasks ||Download (.pdf) Table 31-5 Examples of Core Demands, Kinetic Chain Relationships, and Outcomes of Specific Sporting Tasks
|Sporting Activity ||Core Demands ||Kinetic Chain Relationships ||Outcome |
|Windmill softball pitch ||Rotational and flexion/extension stability, acceleration, and deceleration of trunk ||Transmission of forces from ground to LEs through trunk to UE to ball ||Velocity, location, rotation of pitched ball (55 to 70 mph); delivery of various types of pitches (drop, rise, breaking ball, etc) |
|Gymnastics: vault event ||Rotational and flexion/extension stability; power with punch from horse ||Transmission of forces from horse to UEs through trunk to propel body in airborne positions ||Conversion of horizontal energy to vertical; speed, position, and trajectory of body through space |
|Tennis serve ||Rotational and flexion/extension stability; acceleration and deceleration of trunk ||Transmission of forces from ground to LEs through trunk to UE through racquet to ball ||Velocity, location, spin of served ball (80 to 120 mph); delivery of various types of serves |
|Swimming: butterfly stroke ||Flexion/extension stability ||Transmission of forces from UEs to trunk to LEs to team with butterfly kick ||Efficient propulsion of body through water, avoid excess trunk flexion and extension |
|Volleyball serve ||Rotational and flexion/extension stability; acceleration and deceleration of trunk ||Transmission of forces from ground to LEs through trunk to UE to ball ||Velocity, location, rotation of served ball; various types of spins and serves (floater, topspin) |
A wide variety of movements are associated with sport performance; therefore, athletes must possess sufficient strength and dynamic motor control of the core in all 3 planes of movement (transverse, frontal, sagittal).167 Core stability is vital to athletic performance and especially important for the female athlete. In a study of male and female runners, females were found to have greater hip adduction, hip internal rotation, and tibial external rotation movements during the stance phase of running. Ferber et al102 believe that gender differences in lower-extremity kinematics place greater demands on the core musculature of female athletes. Additionally, core stability may even be more vital for the female athlete as a result of her overall decreased total extremity strength as compared to her age-matched male participant.65 Documented differences in proximal strength measures in female athletes suggest that females may have a less-stable base upon which torque and force can be generated or resisted. This “lack of core stability” is a possible contributor to lower-extremity injury.119,149 Although important energy has been devoted to prevention of ACL and other knee injuries in the female athlete, the sports physical therapist must broaden his/her focus to the body as a whole and include core strengthening activities as a part of preparatory training for all female athletes.
Reviewing and considering the anatomy of the core allows the sports physical therapist to best understand principles of injury and rehabilitation (refer to Chapter 15). Stability of the core requires both passive (offered by bony and ligamentous structures) and dynamic stiffness (offered by coordinated muscular contractions). A spine without the contributions of the muscular system is unable to bear essential compressive loads and remain stable.187 Anatomists have known for decades that a compressive load of as little as 2 kg causes buckling of the lumbar spine in the absence of muscular contractions.201 Likewise, significant microtrauma of the lumbar spine occurs with as little as 2 degrees of rotation, demonstrating the vital stabilizing function of the muscles of the lumbar spine.110,116 Core stabilization is important not only for protection of the lumbar spine but also to resist the reactive forces produced by moving limbs that are transmitted to the spine and other muscles of the core.193
Contemporary research has illuminated the roles of two important local muscle groups: the transversus abdominis (TA)75,136,137,139 and the multifidus.134,287 The TA—deepest of the abdominal muscles—uses its horizontal fiber alignment and attachment to the thoracolumbar fascia to increase intraabdominal pressure, thereby making the core cylinder as a whole more stable. Although increased intraabdominal pressure is associated with the control of spinal flexion forces and a decrease in load on the extensor muscles,278 it is probable that the TA is most important in its ability to assist in intersegmental control240 by offering “hooplike” cylindrical stresses to enhance stiffness and limit both translational and rotational movement of the spine.100,192 Bilateral contraction of the TA performs the movement of “drawing in of the abdominal wall”258 and does not produce spinal movement. The TA is active throughout the movements of both trunk flexion and extension, suggesting a unique stabilizing role during dynamic movement, different from the other abdominal muscles.75,76,193 Also, EMG evidence suggests that the more internal muscles of the trunk (TA and internal obliques) behave in an anticipatory or feed-forward manner to provide proactive control of spinal stability during movements of the upper extremities,137,138 regardless of the direction of limb movements.138 This is important to remember when treating the athlete whose sport is heavily reliant on the upper extremity such as softball, swimming, gymnastics, and volleyball.
Mechanisms of Injury to the Core
Many potential mechanisms of injury exist for the athlete. Cholewicki et al66 suggest that a common factor for injury to athletes may be the inability to generate sufficient core stability to resist external forces imposed upon the body during high-speed events. Other authors suggest a deficient endurance of the trunk stabilizing musculature that predisposes the athlete to traumatic forces over time,241 and motor control deficits and imbalances of the local muscles (TA and multifidus) and the global musculature (rectus abdominis and erector spinae) that occur during performance of functional activities. A weak core could result in inefficient movements, altered postures, and an increased potential for both macro- and microtraumatic injury.65
Two examples of microtraumatic injuries that occur in the female athlete are spondylolysis and spondylolisthesis. The athletic population is more prone to these conditions and more likely to be symptomatic from these injuries. Spondylolytic microfracture of the pars is believed to happen as a result of shear forces occurring during repetitive flexion and extension.275 Athletes with high rates of this type of microtraumatic injury include gymnasts,99 divers, figure skaters, swimmers who perform the butterfly stroke,275 and volleyball players,99 as a result of extreme extension/flexion reversals in trunk posture demanded by these sports. In fact, gymnasts younger than age 24 years have 4 times greater incidence of spondylolysis than the general female population.275 Microtraumatic injuries may occur from muscular imbalances or uncontrolled shear forces acting on the spine,123,275 or because of lack of muscular control and stabilization offered by the core stabilizers. Sports, such as golf, diving, and softball, have the potential for microtraumatic injury to the core to be induced similarly, but related to extremes of rotation, often in combination with extension. Careful assessment of motor strategies and subsequent corrective movement retraining by the sports physical therapist may be a key to prevention of many microtraumatic injuries.
Leetun et al167 found that male athletes had statistically greater core stability scores on tests of hip abduction, hip external rotation, and the side bridge when compared to female athletes (Figure 31-15).167 Athletes who experienced injury to the core (spine/hip/thigh), knee or ankle, and foot during an athletic season demonstrated lower core stability measures than those who did not.167 Again, this leads the sports physical therapist to consider core strength, endurance, and motor performance training as a possible intervention for prevention of injury, especially for the female athlete.
Rehabilitation and Treating the Core
Simple, reliable, and objective clinical test procedures for dynamic motor control of the core are not readily available. Clinically, therapists utilize manual muscle tests that examine isometric holding of muscles, some positional holding tests (the plank or side plank) for endurance in isometric positions, and pressure biofeedback to assess the ability of a patient to hold the core stable during some dynamic tasks. A clinical test for the multifidus was devised that involves the activation of the multifidus at various segments under the palpating finger of a therapist.241 This is performed in the prone position using the command “gently swell out your muscles under my fingers without using your spine or pelvis. Hold the contraction while breathing normally,” 241, p. 116 including side-to-side comparison to assess for segmental activation or inhibition. For many excellent examples of core strengthening exercises, refer to Chapter 15. To make these exercises more specific to your female athlete, incorporate these concepts while performing training programs for other regions. For example, for a swimmer, the therapist may have the athlete lie prone on a swiss ball while performing Thera-Band movements mimicking the pull-through phase. The ball introduces an unstable base to challenge the core muscles.
Knowledge and application of core stabilization will benefit female athletes in all sports at all levels by improving performance, increasing athleticism, and decreasing the potential for injury to the spine and extremities. To provide an optimal, comprehensive exercise program for all female athletes, functional core exercises should be implemented into the female athlete’s sports-specific program.
Special Considerations Concerning the Shoulder in the Active Female
Are women more prone to shoulder injuries? This question does not have ample research to be answered conclusively. Most studies do not separate shoulder injuries by gender or separate general injuries from specific ones. In 2001, Sallis et al249 compared sports injuries in men and women and failed to show a significant difference in overall injury rate. However, these authors reported that in all sports, women reported a higher rate of hip and shoulder injuries. A significant difference was found with a higher rate of shoulder injuries in female swimmers compared to their male counterparts. Yet, the training for female and male swimmers differed greatly, so it is difficult to draw any specific conclusion.249 The training regimen, their structural build, and/or presence of laxity may have predisposed the athletes to overuse injuries. Conclusions are unable to be drawn, until more controlled, specific research is carried out.
Other studies have described differences in various injuries between genders. Kroner and Lind162 found no difference in shoulder dislocations between genders. All shoulder dislocations were recorded over a 5-year period in an area within a population of 253,753 athletes. Of this population, 53.3% of shoulder dislocations occurred in males and 46.7% occurred in females. However, a notable difference occurred between the age group where the peak incidence occurred. Males were 21 to 30 years old, and females were 61 to 80 years old. The injury in the older age group was typically caused by a fall on an outstretched arm.162
A high incidence of shoulder impingement is reported in female softball players286 and both genders of volleyball players.32,53 The shoulder was also the most commonly injured upper-extremity joint in both genders during alpine skiing.254
Clinical experience might suggest that women in general are more flexible and demonstrate increased laxity of their joints when compared to men. Are women more at risk for shoulder injuries because of laxity? First, it is important to describe the difference between laxity and instability. Laxity is not synonymous with instability. Laxity is the physiologic motion that allows for normal ROM. Instability is the abnormal symptomatic motion that results in pain, subluxation, or dislocation.55
There are many general joint laxity tests in literature, the most well known are those by Carter and Wilkinson,62 which have been modified by Beighton42 (Table 31-6 and Figure 31-16). These tests examine ROM at the trunk (single test) and knees, fingers, thumbs, and elbows bilaterally and assigns a point system (0 to 9; a score greater than 5 = diagnosed as hypermobile). Other hypermobility tests have not been proven reliable and valid. Consequently, many studies found in literature regarding general laxity differences between genders are not valid. Of the studies in literature, only 1 utilized the 0 to 9 Beighton scale examining generalized mobility in adolescents.83 The authors reported that of 264 adolescent athletes, 22% of all females and 6% of all males tested were generally “hypermobile.” However, it would be incorrect to conclude from this study that generalized laxity correlates with shoulder laxity. The astute clinician can and should recall the structural and physiologic differences between the genders and take into account clinical experience in order to rehabilitate the female athlete’s shoulder in a multifaceted way.
Table 31-6Generalized Joint Laxity Tests ||Download (.pdf) Table 31-6 Generalized Joint Laxity Tests
|Carter and Wilkinson ||Beighton et al |
Passive thumb apposition to forearm
Passive finger hyperextension so finger parallel to forearm
Elbow hyperextension >10 degrees
Knee hyperextension >10 degrees
Excessive ankle dorsiflexion and foot eversion
Passive hyperextension of small finger >90
Passive thumb apposition to forearm
Elbow hyperextension >10 degrees
Knee hyperextension >10 degrees
Trunk flexion, knee extension, and palms flat on floor
Hypermobility screening maneuvers, as developed by Carter and Wilkinson and modified by Beighton et al.
Softball, swimming, and gymnastics are 3 sports that emerge when considering the female athlete. There is a high incidence of injury in both genders when considering softball/baseball, swimming, and gymnastics. Softball is discussed separately because of the difference in the pitching delivery and the differences in rules regarding number of allowable pitches. Swimming is discussed separately because of the extreme high numbers of shoulder injuries that occur in female swimmers. Finally, the sport of gymnastics is described in relationship to its injury potential in females.
Shoulder Injuries in the Windmill Softball Player
Little research has focused on softball pitching biomechanics or injury rates sustained by pitchers. Yet, softball was the team sport with the greatest participation in the United States in 1995. In 1996, Plummer234 reported softball as one of the fastest growing sports for women at the college and high school levels. In fact, in the most recent school year data, softball was the high school sport with the fourth greatest female participation rate, following only basketball, outdoor track and field, and volleyball.6 When comparing the sport of softball to baseball, it is very similar in many demands and functional tasks. Although the softball playing field is smaller, the reaction time for a batter is directly comparable to baseball. The biggest difference between baseball and softball exists in pitching. The softball mound is flat instead of elevated as in baseball. The distance from home plate to the pitching rubber is 40 ft for youth softball and 60 ft 6 in for baseball. A baseball weighs 5 oz in comparison to a softball that weighs 6¼ to 7 oz.37 The delivery of the pitch also differs significantly between the windmill pitch in fast-pitch softball and the overhand release in baseball or general overhead throwing. Similar musculature is used, but in a very different order and with different mechanics (see Figure 31-17),286 with the biceps being more active in the softball pitching motion (38% maximum voluntary isometric contraction) than the overhead throwing motion (19% maximum voluntary isometric contraction).243,259
Six phases of pitching a baseball (A) and three named phases of pitching a softball (B)
REL, ball release; SFC, stride foot contact; TOB, top of the backswing. (A. Reproduced, with permission, from Fleisig GS, Andrews JR, Dillman CJ, Escamilla RF. Kinematic and kinetic comparison between baseball pitching and football passing. J Appl Biomech. 1996;12:207-224; and B. Reproduced, with permission, from Werner SL, Guido JA, McNiece RP, Richardson JL, Delude NA, Stewart GW. Biomechanics of youth windmill softball pitching. Am J Sports Med. 2005;33(4):553.)
In a review of the existing literature, only 4 studies have addressed female softball injury incidence and prevalence. Results suggested that 63% to 80% of all injuries were in the upper extremity and 37% to 50% of the pitchers studied had a time-loss injury in 1 season.135,257,274,286 Furthermore, there were 5.6 injuries per 1000 athlete exposures in softball compared to 4.0 injuries per 1000 athlete exposures in baseball, 63% of which involved the shoulder. Marshall et al described overuse of the shoulder as among the most common injury in female collegiate softball players.188 Based upon these statistics and clinical experience, it would seem prudent to investigate injury prevention strategies.286
Likewise, there are only 2 published studies on windmill pitching biomechanics, as compared to numerous studies on baseball pitching biomechanics. In these studies, it is reported that shoulder distraction forces are similar to those found in overhand pitching. Barrentine et al37 reported that maximum distraction stresses at the shoulder (98% body weight) were reached at 77% of the delivery phase and maximum compressive force at the elbow (70% body weight) occurred at the end of the delivery phase. The difference between baseball and softball pitching is the phase of pitching during which the distraction forces occur, and the position of the humerus during the pitch. In windmill pitching, maximum distraction forces at the shoulder occur during acceleration, whereas maximum shoulder distraction forces for baseball occur during windmill pitching. Shoulder distraction forces occur when the humerus is in a slightly flexed position while controlling internal rotation and elbow extension during acceleration, before ball release. Notably, centrifugal distraction force on the glenohumeral joint is accentuated because the elbow remains in full extension during most of the circumduction motion. For overhand pitching, maximum shoulder distraction forces occur when the humerus is rotated internally and horizontally adducted while maintaining a position of abduction during deceleration after ball release. The biceps labrum complex and the rotator cuff are both at risk for overuse injury at these phases. Conversely, medial elbow injuries are reported less frequently in softball pitching compared to baseball, likely because of the small amount of varus torque produced during the windmill motion.37
It is interesting that a softball pitcher may pitch any number of consecutive innings and games, while baseball pitchers are carefully monitored and often restricted in number of pitches and innings they are allowed to throw. Softball pitchers can throw 1200 to 1500 pitches in a 3-day period as compared to 100 to 150 for baseball. A reason for this seems related to the traditional belief that softball windmill pitching forces were much less in the shoulder and elbow than that of the baseball pitch.286 This is may be true for the amount of varus torque at the elbow, but not for the distraction forces at the shoulder.
Werner et al286 studied the biomechanics of 53 female windmill pitchers, ages ranging from 11 to 19 years. Statistically significant different ranges of motion were found, including greater shoulder external rotation and decreased internal rotation in the dominant arm. What remains unknown is whether these ROM differences are a result of the windmill biomechanics or the concurrent demands of overhand throwing, which is also a big part of softball. Elbow-carrying angle and hyperextension were found to be similar bilaterally. Maximum elbow and shoulder distraction forces were 46% body weight and 94% body weight, respectively.
This study along with the study conducted by Barrentine et al37 show that the compressive forces at the elbow and the distraction forces at the shoulder are similar to baseball pitchers. Thus, allowing softball pitchers to throw an unlimited number of pitches is subjecting them to potential forces of sufficient amplitude to cause overuse injuries. With such high magnitude of shoulder distraction stress and rapid deceleration of the humerus near ball release, the posterior rotator cuff is at high risk for injury, as is the biceps labrum complex, because of the combination of shoulder distraction stress and elbow extension torque.286 With overuse, eccentric muscle loading of the posterior muscle girdle can cause stretching of these muscles allowing dynamic anterior instability of the humeral head.41 When rehabilitating softball pitchers, it is important for the clinician to understand the stresses and forces present during pitching. Educating coaches and athletic trainers regarding these findings is also necessary for injury prevention. An important implementation for windmill pitching injury prevention may be to establish a pitch count as is traditional in baseball.
Rehabilitation and Return to Play
It is important to know the demands of the sport of softball for efficient rehabilitation. The game requires the same demands of baseball for the overhead throw, hitting, running, cutting, quick bursts of acceleration and deceleration, sliding, and catching. The difference in rehabilitation occurs with the differences in the demands of pitching compared to baseball pitching. In the windmill pitch, the pectoralis major is an important contributor to the power of the pitch and also acts as a stabilizer against anterior forces. The subscapularis helps the pectoralis major in its role as a stabilizer. The serratus anterior is a scapulohumeral synchronizer.177 The teres minor is also found to be very active in decelerating the humerus. These muscles should be highlighted in the rehabilitation program along with the standard return-to-throwing rehabilitation.
Core strengthening is also a key factor in return to play for the softball player. The demands on the core during throwing and hitting cannot be ignored. The transfer of energy from the ground through the limbs to core must provide a stable base for the upper extremities to function properly.142
Consequently, rehabilitation and return to play for the windmill softball pitcher may include some variations to the typical softball or baseball rehabilitation program that does not require the windmill motion in the athlete’s return to playing. As with any overhead athlete, it will be important to restore a balance of stability and mobility in the shoulder, with a strong, stable core. It is also important to strengthen scapular stabilizers as one would in any overhead athlete rehabilitation program. For the windmill pitcher, it may be more effective to include specific functional activities highlighting the demands of the pitch when acute pain and inflammation have subsided. Functional exercises that the authors of this chapter like to use are summarized in Table 31-7 with Figures 31-18 to 31-33 to demonstrate the techniques. These exercises are functional and windmill-pitch specific.
Table 31-7Sample Functional Exercises for Return-to-Windmill Pitching ||Download (.pdf) Table 31-7 Sample Functional Exercises for Return-to-Windmill Pitching
|Exercise ||Muscles Affected ||Targeted Pitching Phase Cycle |
|Trunk rotation with biceps curl (see Figure 31-18) || ||End of SFC to REL |
|Lawn mower with external rotation (see Figure 31-19) || ||SFC to REL |
|Step up/arm lift/hip extension (see Figure 31-20) || |
|First 25% of pitch delivery (up to TOB) |
|Chest press on swiss ball with serratus punches (see Figure 31-21) || |
|Pectoralis major is a key muscle in power of entire pitch cycle and stabilizes against anterior sheer forces |
|Step up with hip ER/IR (see Figure 31-22) || || |
|“Full can” in tall kneeling on DynaDisc or BOSU ball (see Figure 31-23) || |
|SFC → REL |
|Physioball deceleration throw with therapist (see Figure 31-24) || ||Just after SFC → REL |
|Lunging with military press (see Figure 31-25) || |
LE—Quadriceps, hamstrings, hip extensors, and rotators
UE—Shoulder external rotators, deltoids, latissimus dorsi
|No specific phase |
|Push-up plus progression (see Figure 31-26) || ||Pectoralis and serratus active through entire cycle |
|Shoulder IR with Thera-Band sitting on swiss ball (see Figure 31-27) || ||Beginning → SFC |
The trunk rotation with a bicep curl (see Figure 31-18) mimics the motion required in the trunk and arm near and at ball release. The Thera-Band provides resistance for trunk facilitation/control while the weight in the hand provides concentric and eccentric strengthening for the shoulder extensors/flexors and biceps.
Trunk rotation with biceps curl
A. Start in stride stance facing sideways, front foot pointing forward, back foot pointing sideways with Thera tubing wrapped around waist and secured at shoulder (to resist rotation). B. Weight in dominant/pitching hand. Perform a bicep curl while rotating trunk forward.
Lawn Mower with external rotation
A. Stance, forward flexion at waist with weight in hand. B. Retract scapula like a rowing motion, adding external rotation at the end.
The step-up with ipsilateral arm raise and contralateral hip extension (see Figure 31-20) synchronously fires the latissimus dorsi and hip extensors. At the beginning of the pitch delivery, the dominant leg remains in a closed chain, neutral hip position. The hip then travels into extension, which is mimicked in the step up. During the first 25% of the pitch delivery phase, the latissimus dorsi is very active.
Step up/arm lift/hip extension
Step onto step with dominant leg (right for right-handed pitcher) and lift ipsilateral arm into flexion with weight while left leg raises into hip extension.
The chest press on a Physioball with serratus punch (see Figure 31-21) challenges the core, as it has to stabilize the trunk on the ball while strengthening the pectoralis major, which is a key muscle in the power of the pitch and a major stabilizer against anterior sheer forces. Although not positionally correct for the softball pitch, this exercise incorporates the serratus anterior, which is important to strengthen as the scapula must provide a strong, stable base.
Chest press on Physioball with serratus punch
A. Lie on back over ball, feet shoulder width apart, dumbbells in both hands. Start with elbows bent, weights at chest. B. Straighten elbows pressing weights together, at the end of the motion add scapular protection.
The step-up with closed-chain hip external and internal rotation (see Figure 31-22) trains the hip and core in the similar motions the hip passes through from beginning of wind up (step-up phase), before and during stride foot contact (hip external rotation), and at delivery phase when the pelvis is closing and the hip goes into internal rotation.
Step up with closed chain external rotation/internal rotation
Step up onto step with dominant leg, keep other leg in slight hip flexion with knee flexion (A). Slowly rotate into internal rotation and external rotation on dominant leg. (B, external rotation shown.)
In Figure 31-23, the athlete is strengthening the shoulder elevators (full can position) while challenging the core at the same time. This is important to provide excellent humeral steering, balance the strong internal rotators, and also it is important in the overhead throw, as the pitcher must also participate in defensive plays. Thus, the lunge with military press (see Figure 31-25) can also assist in trunk/lower extremity control while overhead shoulder stability is maintained, and double as the top of backswing movement.
Full can, tall kneeling on DynaDisc or BOSU ball
Start in tall kneeling position on balance challenging surface. Raise weight at 45-degree angle with thumbs up, within comfort range. Emphasize good trunk alignment throughout exercise.
Plyoball deceleration throw (see Figure 31-24) helps to strengthen the shoulder concentrically and eccentrically mimicking the last portion of the pitching cycle. The push-up “with a plus” exercise (see Figure 31-26) is important as the pectoralis and the serratus anterior are muscles active throughout the entire pitching cycle.
Plyoball deceleration throw with therapist
Standing in stride stance facing sideways, horizontally abduct the shoulder and extend the elbow. Therapist tosses Plyoball; athlete catches (A) while simultaneously rotating pelvis forward and bringing ball through (B), flexing the shoulder and elbow (mimicking delivery and follow through) (C); then reverse the same motion and athlete tosses back to therapist with shoulder and elbow extended (ie, reverse sequence from C→B→A). Focuses on concentric and eccentric training. Have athlete mimic her delivery as much as possible.
Lunging with military press
A. Start with legs straight, elbows bent, hands shoulder height. Raise arms overhead, extending elbows; as arms raise overhead, perform lunge. B. Return to starting position.
Wall push-up “plus”
A. Hands shoulder width apart, flex elbows as lower down to wall. B. Extend elbows and at end of exercise add an extra push (plus) into scapular protraction. Progression: at wall, at table, on floor, hands on wobble board or BOSU ball, feet on Physioball, hands on floor. Note poor trunk positioning on left.
Thera-Band shoulder internal rotation on Physioball
While sitting on Physioball and facing away from door, grasp Thera-Band at shoulder height. In the 90/90 position (A), pull band forward into internal rotation (B). May also train external rotators by facing wall and pulling opposite direction.
The S-shaped curve in pull-through
(Adapted from Pink M, Perry J, Browne A, Scovazzo ML, Kerrigan J. The normal shoulder during freestyle swimming. An electromyographic and cinematographic analysis of twelve muscles. Am J Sports Med. 1991;19:574.)
Phases of the freestyle swimming stroke cycle
(Adapted from Pink M, Perry J, Browne A, Scovazzo ML, Kerrigan J. The normal shoulder during freestyle swimming. An electromyographic and cinematographic analysis of twelve muscles. Am J Sports Med. 1991;19:569-576.)
Return to pitching should be gradual with a progression of percent effort as well as number of pitches. Refer to Appendix B for a return-to-windmill pitching program. A return-to-throwing program is also included in Appendix C. The return-to-throwing guidelines should be modified to the specific athlete. Is she an exclusive pitcher who only needs to make shorter overhand throws to the bases? Or does she also play another position when not pitching, that is, outfield or infield? This should be a factor in the decision making regarding the final distance at which the softball player performs the throwing program. For example, an exclusive pitcher is not going to need to spend time at the 120 ft and 150 ft stage; more time would be focused on specific windmill exercises and shorter overhand throwing.
More research is needed in the area of windmill pitching as well as educating coaches and players in the potential risk of injury with overuse. Clearly, current research is showing forces at the shoulder to be much higher than once believed. The active female can perhaps decrease the risk of suffering from an overuse shoulder injury by following pitch guidelines closer to that of a baseball pitcher and performing a windmill-specific exercise routine.
Shoulder Injuries in Female Swimmers
There is insufficient research to conclusively report that female swimmers actually sustain shoulder injuries at a higher rate than male swimmers. Most studies are not gender specific when injuries to the upper extremity are reported.15,231,285,291,292 It is evident, however, that differences exist between males and females in anatomy, upper-body strength, and laxity, as previously discussed. Therefore, with high numbers of shoulder injuries reported in swimming,285 it is important for the sports medicine personnel to understand the demands and risks that the sport imposes.
Swimming has become a very popular recreational and competitive athletic activity. Triathlons are becoming increasingly popular as well, and swimming is 1 of the 3 components. Ninety percent of complaints by swimmers that are significant enough to seek medical attention pertain to the shoulder.285 Sport-specific demands of swimming include increased shoulder internal rotation and adduction strength, increased shoulder ROM, and endurance of the shoulder complex. During the freestyle stroke, most of the forward propulsion is produced by the upper body, the legs help minimally (Figures 31-34 and 31-35). Specifically, the shoulder adductors and extensors (pectoralis major and latissimus dorsi) should be assessed. These same muscles produce internal rotation. Increases in adduction and internal rotation can lead to muscle imbalances, which can reduce glenohumeral stability and provide optimal conditions for impingement. Freestyle is used 80% of the time during the swimmer’s training, regardless of what stroke the athlete uses competitively.15 Therefore, impingement poses a potential problem to all swimmers.
As mentioned previously, swimming requires shoulder ROM greater than that of nonswimmers in order to excel. This increased motion allows for longer stroke length, which directly correlates to a swimmer’s speed. Although the increased ROM is beneficial to performance, it can be detrimental to glenohumeral stability. Excessive ROM produces capsuloligamentous laxity, which decreases the force produced by the rotator cuff muscles to provide stability.285
The third specific demand includes the incredible endurance necessary of the rotator cuff and scapular stabilizers. The teres minor, infraspinatus, and subscapularis are rotator cuff muscles that fire continuously through the swimming cycle. The scapular stabilizer that also fires continuously is the serratus anterior. These muscles are at risk for fatigue with resultant possibilities of impingement or instability/subluxation of the shoulder. The repetitive nature of swimming predisposes the participant to overuse injury from microtrauma and mechanical primary impingement. This can ultimately lead to instability, rotator cuff fatigue, and resultant secondary impingement.15 Swimmers average 8000 to 20,000 m of training per day and may practice twice a day, with no rest days in between. This subjects the shoulder complex to an incredibly high number of stroke repetitions. An average competitive swimmer may swim 10,000 m per day. Thus, an athlete who swims 20 cycles per 50 m (estimated for the average swimmer), completes 4000 repetitions per shoulder, every day.15
Unpublished data from Centinela Hospital Medical Center Biomechanics Laboratory report that swimmers exhibited a higher incidence of positive Hawkins test than positive Neer tests for shoulder impingement.232 The Hawkins test analyzes compression of the rotator cuff tendons under the acromion, whereas the Neer test analyzes the pinching of the rotator cuff undersurface on the anterosuperior glenoid rim. This may indicate that swimmers tend to display more problems with compression of the cuff tendons under the acromion rather than undersurface tears. EMG studies reveal swimmers with painful shoulders have altered muscle-firing patterns when compared to swimmers with no shoulder pain. The serratus anterior has decreased muscle activity and the rhomboids have increased activity from the nonpainful shoulders, during mid pull through. If the serratus anterior is not functioning properly to aid in scapular upward rotation and protraction, then the acromion would also lack upward rotation placing the swimmer at risk for compression of the cuff tendons under the acromion.
Interestingly, the rhomboids are an antagonist muscle to the serratus anterior. When the serratus anterior fatigues, there is no other muscle that can help produce the same action. The antagonist muscle is called upon to help stabilize the scapula creating a disturbance in the synchrony of normal scapular rotation during propulsion.
As previously noted, the serratus anterior and subscapularis fire continuously throughout the freestyle stroke. The serratus anterior is firing continuously to provide a stable base for the humerus, and the subscapularis is firing caused by the humerus being in predominately internal rotation throughout the stroke. These 2 muscles are susceptible to injury because of fatigue.232
In a similar example, the same research documented that the subscapularis (an internal rotator) had decreased muscle activity and the infraspinatus (an external rotator) is found to have increased muscle activity compared to normal at mid recovery in painful shoulders. Again, the antagonist muscle is called upon when fatigue has occurred in the agonist causing potential imbalances and asynchronous movement. Another method to encourage the subscapularis to diminish its activity could be to avoid the extreme ranges of internal rotation motion avoiding impingement.232
Three-dimensional videography was used by Yanai and Hay292 to determine when, during the swimming motion, the shoulder experienced impingement. During the front crawl in swimming, on average, impingement occurred during 24.8% of the stroke time. However, each subject monitored experienced impingement in some cycles and not others. This suggests that stroke technique may play a factor in susceptibility to impingement.292 Some studies show that between 50% and 70% of the time, shoulder pain was reported during pull through;78,242 others, however, report impingement occurs more often during the recovery stage.291,292 During early pull-through, the pectoralis major and the teres minor are highly active, with their activity peaking at mid pull-through. The teres minor is the prime contributor to maintaining humeral head congruency in the glenoid because of its insertion closer to the axis of rotation than the pectoralis. In painful shoulders, the most notable difference during pull-thorough was decreased muscle activity of the serratus anterior.232
The hand entry position during freestyle stroke is also reported to be a frequent point of pain in swimmers.291 During hand entry and forward reach, the upper trapezius, rhomboids, and serratus anterior are all active to form a force couple to properly position the glenoid fossa. The supraspinatus and the anterior and middle deltoid are also active to abduct and flex the humerus as the hand reaches forward in the water. Without the supraspinatus, the deltoid proper firing of predisposes the humeral head to excessive movement within glenoid fossa.232
Rehabilitation and Return to Swimming
Shoulder rehabilitation for these female swimmers should be multifaceted. Great emphasis should be placed on restoring normal ROM, strength, and endurance based on the evaluative findings. Table 31-8 lists the typical signs and symptoms of possible causes of swimmer’s shoulder. Exercises should incorporate trunk and hip movements along with both scapular and glenohumeral neuromuscular retraining. Core stability should also be emphasized in the shoulder rehabilitation program as it needs to provide a stable base for the athlete to propel their body forward.
Table 31-8Typical Signs and Symptoms and Possible Causes of Swimmer’s Shoulder ||Download (.pdf) Table 31-8 Typical Signs and Symptoms and Possible Causes of Swimmer’s Shoulder
|Signs and Symptoms ||Possible Cause |
|Postural deformities of rounded shoulders and thoracic kyphosis ||Tightness of the pectoralis minor |
|Weakness of the posterior cuff muscles and scapular stabilizers ||Weakness can be a result of strength imbalances between the anterior and posterior muscles secondary to the demands of the sport and to stretch weakness |
|Limited internal rotation and excessive external rotation ROM ||Tightness of the posterior capsule or posterior cuff muscles which causes a shift in the available ROM |
|Decay of normal scapulothoracic rhythm ||Tightness of the anterior chest musculature and weakness of the scapular stabilizers |
Flexibility and mobilization techniques should reflect the findings from the evaluation. Importance should be given to restore normal ROM without compromising stability. The most typical restrictions are found in the posterior portion of the glenohumeral joint capsule or tightness of the posterior rotator cuff muscles.285 Swimmers, in general, tend to spend more time stretching their anterior capsule. This results in loss of internal rotation and horizontal adduction. Horizontal adduction may be improved by stabilizing the scapula on the thorax while crossing the arm over the chest. This can be performed at 90 degrees of shoulder flexion and above to address all portions of the cuff. Posterior capsule flexibility is improved by flexing the shoulder to 90 degrees and providing a downward force on the flexed elbow.
Internal rotation ROM, rather than external rotation, at the end range of abduction proves to be important for swimmers. This motion is most important during the late recovery stage of the freestyle stroke. Internal rotation should be stretched at 90 degrees, 135 degrees, and at end-range abduction in stretches assisted by the therapist or utilizing self-stretches such as the “sleeper stretch.” External rotation stretching should still be carried out if it is lacking. Other important muscles to check for normal flexibility include the pectoralis major and minor, upper trapezius, levator scapulae, biceps, triceps, and serratus anterior. Swimming strokes do not happen in a straight cardinal plane of motion; during the arm cycle, there are multiple combinations of movements taking place.15 A flexibility program can be creatively structured with this in mind.
Strength and Endurance Training
Development of a strength and endurance training program should focus on restoring normal balance to the anterior and posterior shoulder musculature. It also should focus on restoring equilibrium between scapular and humeral movements. It is important to remember that increased adduction and internal rotation strength is unavoidable in swimmers. To avoid muscular imbalance, emphasis on rotator cuff exercises with importance on external rotation strength is beneficial.285 The 3 primary considerations in a strengthening program are (a) isolate the rotator cuff and scapular muscles, (b) implement endurance-based exercises, and (c) include sports-specific functional exercises.15 Table 31-9 provides primary considerations and rationale for developing a strengthening program for swimmers.
Table 31-9Considerations and Rationale in a Strengthening Program for Swimmers ||Download (.pdf) Table 31-9 Considerations and Rationale in a Strengthening Program for Swimmers
|Primary Considerations ||Rationale |
|Isolation of the rotator cuff and scapulohumeral muscles (correctly train prime movers/stabilizers, not antagonists) ||EMG studies demonstrate cuff muscles act independent of each other during the stroke cycle |
|Muscular endurance, high repetitions of specific exercises (sprint, middle-distance, or long-distance swimmer—should reflect in number of repetitions given) ||Swimming involves excessive repetition and muscular endurance; 3 sets of 10 repetitions are inadequate |
|Sports-specific function ||Exercises specific to the swimmers stroke and body postures help return to sport as efficiently and quickly as possible |
Female swimmers appear to be highly susceptible to secondary impingement as a consequence of flexibility, strength, and muscular endurance factors discussed earlier. Please refer to Chapter 20 for details on primary and secondary impingement. Table 31-10 provides basic guidelines for progression of treatment for swimmer’s shoulders with 2-degree impingement. The initial goal in the rehabilitation program is to establish a stable scapular base and strengthen the rotator cuff muscles in a neutral position.255 Phase II introduces exercises up to 90 degrees. In Phase III, overhead exercises can be initiated with functional training. Phase IV is gradual return to athletic activity, progressing in speed and distance.15 Most swimming programs emphasize only upper-extremity strengthening and function. Challenging core stability during some upper-extremity exercises is beneficial to the athlete. Swimming is a chain of events involving the arms, trunk, and legs together. Focusing solely on the shoulder complex fails to address all areas of the kinetic chain vital to swimming efficiency and performance.
Table 31-10Basic Guidelines for Progression of Treatment for Swimmer’s Shoulders with a 2-Degree Impingement ||Download (.pdf) Table 31-10 Basic Guidelines for Progression of Treatment for Swimmer’s Shoulders with a 2-Degree Impingement
|Phase I |
Modalities PRN for pain control
Address ROM losses
Rotator cuff strengthening at 0 degrees abduction, with towel support
Scapulothoracic muscle in neutral
Prone arm raise at 0 degree abduction
Scapular retraction (row)
Prone ball roll (for lower trap)
Prone ball stabilization on floor
|Phase II (0 to 90) |
|Phase III—Functional training |
Full range flexion and abduction strengthening
Combined movement patterns
Swim bench (if available)
Proprioception and Functional Training
Retraining joint proprioception in freestyle swimmers, and all athletes, is important. Are differences seen in swimming stroke patterns with painful shoulders intentional changes to avoid pain, or caused by inadequate feedback from joint receptors from capsular damage? Multiple studies have shown proprioceptive deficits in subjects with glenohumeral joint multidirectional instability.35,47,89 However, no studies specific to symptomatic swimming athletes are available. Proprioception is derived from both conscious and unconscious components, as was previously described in detail in other chapters. Making the athlete consciously aware of humeral and scapular position during strength training and swimming may help to improve conscious proprioception. However, only conscious training is not enough, unconscious neuromuscular output is also vital to athletic performance. Training unconscious proprioceptive awareness can be carried out with plyometric training.15
Plyometric training is used to not only enhance power and explosiveness but may also help improve “synchrony of movement that is needed for the swimming stroke.” 15, p. 315 Progression of an upper-extremity plyometric training program for swimmers should include progressing the degree of shoulder abduction (starting in more neutral positions increasing to overhead); progressing the weight of the medicine ball; and increasing speed, repetitions, and difficulty.
Closed-chain exercises can be useful in rehabilitation of the swimmer because they mimic how the body is pulled over the arms during pull through, while engaging the trunk and core muscles for stabilization.15 For example, in Phase III, a Thera-Band can be used to provide resistance mimicking the pull through phase while the athlete is prone over a Physioball (see Figure 31-30). This forces the core muscles to stabilize the athlete’s body as her arm is going through a specific motion. During this exercise, it is important to keep the shoulder at 90 degrees of abduction to ensure proper mechanics and avoid impingement. Internal obliques are also important muscles to strengthen because of the rotation required at the trunk for the swimmer to body roll during freestyle. If core muscles are weak or lack endurance, they will not provide a stable base for the upper extremities. As discussed in several contexts, but especially important in the swimmer, a weak core can be a contributing factor in a shoulder injury.119,149
Prone swimming exercise on ball
A. Start position. B. Internal rotation or during pull through. C. Finish position. Note: performing this exercise prone on the ball increases sport position specificity and demands on the core musculature.
Throughout the rehabilitation program, it is feasible for the athlete to continue swimming with use of swimming aids (ie, kickboard held under the body), modification of yardage, and altered rest time. This active rest concept is dependent on the severity and nature of shoulder injury and should be athlete and injury specific. For example, an impingement injury caused by fatigue of the posterior cuff muscles may still respond positively to treatment in conjunction with a significant decrease in yardage and increase in rest time before swimming again to avoid fatigue. It is vital to educate both the coach and swimmer that at the first sign of shoulder pain the athlete is to stop swimming.15
In conclusion, freestyle swimmers can present with signs and symptoms of either instability or impingement, or a combination of both. The rotator cuff provides stability at the glenohumeral joint and can therefore be a source of pain or disability when instability or impingement occurs. It is essential to provide the optimum environment for the rotator cuff to work effectively by balancing adequate stability with the appropriate mobility in the shoulder complex. Accordingly, for an efficient and effective rehabilitation program, clinicians must have knowledge of the sport-specific skills that are required. Finally, creativity in designing the rehabilitation program to incorporate the core with upper-extremity activities and meet the swimmers’ demands (sprinter, middle, or long-distance swimmer) is essential as well.15
Considerations in the Female Gymnast
The final sport for special consideration in regard to the female athlete is gymnastics. Gymnastics is important to consider because of its high potential for micro- and macrotraumatic injuries, as well as the vulnerability of its athletes to body image issues that are elaborated upon in the female athlete triad section. Certainly, similar considerations may exist in sports not mentioned; however, it is beyond the scope of this chapter to attempt to cover all sports in which women participate.
Multiple injuries occur in gymnasts of all ages and ability levels, whether recreational or competitive. Women’s gymnastics involves 4 apparatuses: beam, floor exercise, vault, and uneven bars. Men’s gymnastics involves 6 apparatuses: floor exercise, rings, parallel bars, pommel horse, vault, and high bar. The demands of this sport include the need for great flexibility, incredible strength, balance, and explosive power. Competitive gymnastics requires intensive training with a large time commitment, usually beginning at a young age. The average junior elite gymnast (age 10 to 14 years) spends more than 5 days per week training, for a total of approximately 25 hours a week.57 Such demand on a young body is not without penalty. The period of rapid growth, which occurs in adolescence, causes the young gymnast to be more susceptible to injury than the postpubescent gymnast.57 Questions also arise in regards to the possibility of stunted or inhibited growth during these vital years of development and maturation.58,277,284
Recently, a Gymnastics Functional Measurement Tool was developed and studied by Sleeper et al.264 This field-based assessment tool was found to correlate with United States Gymnastics competitive level of the athletes and allows sports practitioners to reliably examine and score performance in 10 important physical tasks necessary for participation in gymnastics. Such a sport-specific test battery may assist the clinician to determine readiness for participation in gymnastics and risk for potential injury.
Gymnasts sustain a large variety of injuries. Caine et al57 followed 50 competitive gymnasts over a 1-year period tracking injuries. The most commonly injured regions in the body by order of frequency were (a) the lower extremity (63.7%), particularly the ankle and knee; (b) the upper extremity (20.4%), particularly the wrist; (c) and the spine and trunk (15.2%), particularly the lower back. These findings are consistent with other multiple studies conducted.33,57,172,252,271 Gymnasts were most likely to injure themselves on the floor exercise (35.4%), followed by the balance beam (23.1%), the uneven bars (20%), and, lastly, the vault (13.8%). The remaining 7.7% of injuries were placed under “other,” pertaining to possible warm-up or conditioning periods. The distribution between sudden onset and gradual onset of injury was 44.2% and 55.8%, respectively. Clearly traumatic as well as overuse injuries occur in this sport.
Female gymnasts of today are shorter, lighter, and mature later than their predecessors 30 years earlier. Increased magnitude and intensity of training at an early age has become standard. The question arises whether these external characteristics are a result of self-selection for gymnastics or a result of inadequate nutrition for the level of activity during this crucial period of development.58 Studies suggest that the shorter femoral leg length seen in female gymnasts may be a result of the repetitive compressive stress causing premature closure of femoral and tibial epiphyses.58,59,183,276 A short-term longitudinal study by Mansfield and Emans183 reported that gymnasts advance through puberty without a normal pubertal growth spurt. Catchup growth does occur once the gymnast retires from the sport or significantly reduces training58; however, it is questionable whether adequate growth and normal height are eventually achieved. Longitudinal studies of 1 set of triplets and 2 sets of twins (one gymnast, other one(s) not) reveal significantly later onset of menarche when compared to their nongymnast sibling. In the set of triplets, energy expenditure exceeded energy intake by 600 kcal and the gymnast had lower body weight and percent body fat compared to her siblings.58
Lower levels of hormones and decreased serum growth factors have also been identified in gymnasts. Serum leptin is involved in the regulation of energy intake and energy expenditure. Leptin is secreted by adipocytes and binds to an appetite-stimulating neuropeptide, which produces neurons in the hypothalamus. Leptin levels increase with food intake and decrease during periods of starvation. Low body fat levels have been linked to low levels of leptin. A decline in leptin levels has an effect on the secretion of gonadotropins and sex steroids, which may be a factor in delayed menarche and amenorrhea leading to the female athlete triad, which is discussed in detail later in this chapter.284
Some additional noteworthy considerations in the sport of gymnastics include (a) gymnasts do not wear any type of supportive shoe while training and competing, making it difficult to correct faulty biomechanics at the foot with any type of orthosis; (b) the typical postural salute to judges, and landing of jumps and dismounts, is a hyperlordotic position of the lumbar spine, potentially contributing to trunk instability problems (see Figure 31-31); (c) gymnastics, unlike many sports, has a significant amount of skills and activities performed with the upper extremities in a closed-chain position; and (d) gymnasts jump and land from various heights with twisting and rotational components. With these factors in mind, focus should be placed on balancing strength and flexibility to help correct faulty biomechanics or structural faults; emphasis placed on core strength and stability and education of gymnasts should occur regarding ideal trunk posturing at the beginning and end of routines. Likewise, education on proper jumping and landing must be an integral part of training and rehabilitation. Refer to the section “Anterior Cruciate Ligament Injuries” earlier in this chapter for more detail on jumping and landing.
Typical gymnast pose before/after routines and landing jumps/tumbling moves. Note excessive lumbar lordosis.
Of additional concern are the body image requirements and subsequent disorders common in the sport of gymnastics potentially leading to inadequate caloric intake.58,59,277 Educating the coaches, gymnast, and rehabilitation staff in regard to the female athlete triad potential risks of osteoporosis and stress fractures, as well as stunted growth patterns, is important.
Historical Perspective and Evolution
The female athlete triad (Triad) was first described by Rosemary Agostini, MD, Barbara Drinkwater, PhD, Aurelia Nattiv, MD, and Kimberly Yeager, MD, MPH, in the early 1990s.1,50,96,213, 214 The Triad (see Figure 31-32) was used to describe the connection between 3 independent clinical disorders: eating disorders, amenorrhea, and osteoporosis. Continued research and discussion among sports medicine professionals in varied disciplines led to the American College of Sports Medicine publishing the first Female Athlete Triad Position Statement in 1997.96 The purpose of the position statement was to provide direction for identification, prevention, and treatment of these individual, yet connected, medical disorders in this specialty population.8,19,213, 215
The female athlete triad, as first described in 1997
Evolution of this original concept has continued. Classification of eating disorders such as anorexia nervosa (AN),209 bulimia nervosa (BN), and eating disorders not otherwise specified (EDNOS) were the severe forms of nutritional deficit that were observed. Because a minority of female athletes fit the diagnostic criteria for any of these diseases, the term eating disorders has been expanded to include the concept of disordered eating patterns that encompasses a wide range of harmful nutritional strategies associated with the other factors of the Triad.21,215 Osteoporosis (identified in the original Triad description) has been modified to include osteopenia and the less-severe forms of bone loss more commonly seen in females screened and diagnosed with the Triad. Discussion also ensued regarding the expansion of amenorrhea to include menstrual irregularities and other reproductive dysfunctions that are associated with but independent of amenorrhea. These other dysfunctions are intermittently seen in association with other components of the Triad, and include oligomenorrhea, anovulation, and altered luteal phase length.213, 215 The revised and updated Triad describes the interaction and coexistence of eating disorders/disordered eating behavior, menstrual irregularities, and decreased BMD.215
Further evolution has established a spectrum concept for each of the independent yet interrelated components. The current concept of the Triad refers to the interrelationship between energy availability, menstrual function, and BMD. Each of these components is described and illustrated as a spectrum in the publication of the revised position statement by the American College of Sports Medicine in 2007.215 Each spectrum ranges from the healthiest state to the unhealthiest state of a female athlete in each of these components (see Figure 31-33).
The female athlete triad, as described in 2007
Note the spectra between “optimal health” and “poor health” in the 3 components of the triad.
There is a very important relationship between the amount of calories consumed and the amount of calories expended for any athlete. The spectrum of energy availability ranges from low energy availability with or without an eating disorder to optimal energy availability. Optimal energy availability defined as the appropriate balance of calories; or simply stated: calories taken in versus calories expended. Energy availability is critical for optimal performance, maintenance of body composition, and prevention of health problems.23 For the female athlete, the prevention of health problems includes:
establishing and maintaining normal menstruation39,215
preservation of a strong immune system213
building and repairing muscle tissue and bone23,39
A “negative energy balance” resulting from a sustained negative calorie balance (intake less than output) can be a result of many factors, ranging in decreasing severity from a clinically diagnosed eating disorder to the elimination of a food group, for example, dairy or meat from the diet, to inadvertently not eating enough to keep up with a sudden or unexpected increase in a training schedule. The internal and external pressures to achieve athletic success, attain a body composition of unreasonably low body fat percentage, and/or achieve or maintain unrealistically low body weight often lead to disordered eating patterns and occasionally to clinical eating disorders.11,18-21,39,40
Clinical eating disorders include AN, BN, and EDNOS.39 Each of these disorders have specific diagnostic criteria that are established (Tables 31-11 to 31-13). AN represents the extreme of voluntary starvation with severe caloric restriction and an altered self-image, viewing oneself as overweight when in reality being as much as 15% below of ideal body weight. The prevalence of AN is 0.5% to 1% in adolescent and young adult women as compared to 2% to 4% with BN.23 BN is characterized by a “binge and purge” eating behavior. Binging occurs as a result of physiologic hunger followed by purging to eliminate the caloric intake.23 The purging behavior takes a multitude of forms including vomiting, laxative use, diuretic use, enemas, and excessive exercise.11,19,21,39,40,117,126,152 Physiologic and psychological problems resulting from this purging behavior include fluid and electrolyte imbalances, dehydration, acid-base imbalances, cardiac arrhythmia, the enlargement of the parotid glands, erosion of tooth enamel, gastrointestinal disorders, low self-esteem, anxiety, depression, and reported cases of suicide.19,21,39,40,45,50
Table 31-11Diagnostic Criteria for Anorexia Nervosa (AN) ||Download (.pdf) Table 31-11 Diagnostic Criteria for Anorexia Nervosa (AN)
|A. Refusal to maintain body weight at or above a minimally normal weight for age and height. Weight loss leading to maintenance of body weight <85% of that expected; or failure to make expressed weight gain during period of growth, leading to body weight <85% of that expected. |
|B. Intense fear of gaining weight or becoming fat, even though underweight. |
|C. Disturbance in the way in which one's body weight or shape is experienced; undue influence of body weight or shape on self-evaluation; or denial of the seriousness of the current low body weight. |
|D. In postmenarchal females, amenorrhea, i.e., the absence of at least 3 consecutive menstrual cycles. A female is considered to have amenorrhea if her periods occur only following hormone administration. |
|Specify type: |
|Restricting type: During the episode of anorexia nervosa, the person does not regularly engage in binge eating or purging behavior, i.e., self-induced vomiting or misuse of laxatives or diuretics. |
|Binge eating/purging type: During the episode of anorexia nervosa, the person regularly engages in binge eating or purging behavior, i.e., self-induced vomiting or misuse of laxatives or diuretics. |
Table 31-12Diagnostic Criteria for Eating Disorder Not Otherwise Specified (EDNOS) ||Download (.pdf) Table 31-12 Diagnostic Criteria for Eating Disorder Not Otherwise Specified (EDNOS)
|A. For females, all of the criteria for AN are met, except the individual has regular menses. |
|B. All criteria for AN are met except that, despite significant weight loss, the person's current weight is in the normal range. |
|C. All criteria for BN are met except that the binge eating and inappropriate compensatory mechanisms occur at a frequency of less than 2 per week for a duration of less than 3 months. |
|D. Regular use of inappropriate compensatory behavior by an individual of normal body weight after eating small amounts of food (self-induced vomiting after consumption of 2 cookies). |
|E. Repeatedly chewing and spitting out, but not swallowing, large amounts of food. |
|F. Binge-eating disorder: recurrent episodes of binge eating in the absence of the regular use of inappropriate compensatory behaviors characteristic of BN. |
Table 31-13Diagnostic Criteria for Bulimia Nervosa (BN) ||Download (.pdf) Table 31-13 Diagnostic Criteria for Bulimia Nervosa (BN)
|A. Recurrent episodes of binge eating. An episode of binge eating is characterized by both of the following: |
| 1. Eating, in a discrete period of time, e.g., within any 2-hour period, an amount of food that is definitely larger than most people would eat during a similar period of time and under similar circumstances, and |
| 2. A sense of lack of control over eating during the episode, e.g., a feeling that one cannot stop eating or control what or how much one is eating. |
|B. Recurrent inappropriate compensatory behavior in order to prevent weight gain, such as self-induced vomiting; misuse of laxatives, diuretics or other medications; fasting; or excessive exercise. |
|C. The binge eating and inappropriate compensatory behaviors both occur, on average, at least twice a week for 3 months. |
|D. Self-evaluation is unduly influenced by body shape and weight. |
|E. The disturbance does not occur exclusively during episodes of anorexia nervosa. |
|Specify type: |
|Purging type: The person regularly engages in self-induced vomiting or the misuse of laxatives or diuretics. |
|Non-purging type: The person uses other inappropriate compensatory behaviors, such as fasting or excessive exercise, but does not regularly engage in self-induced vomiting or the misuse of laxatives or diuretics. |
The EDNOS diagnosis includes those individuals who meet every other criteria for AN except amenorrhea/oligomenorrhea or decreased body weight or those individuals who demonstrate all other criteria for BN with a decreased frequency or duration of the purging behavior. This additional category, EDNOS may lead to better detection and treatment of those female athletes who exhibit the criteria for AN but paradoxically maintain “normal” body weight because of the increased lean body mass.19,21,40 Despite the many strides that have been made in the classification of disordered eating, there are a plethora of unhealthy eating behaviors that elude the AN, BN, or EDNOS diagnoses and result in a negative energy balance.
It is difficult to estimate the number of female athletes who demonstrate disordered eating or unhealthy eating habits. Several different surveys have been developed in an attempt to identify collegiate female athletes with disordered eating behaviors. The prevalence of eating disorders ranged from 6% to 60%, depending upon the tool used, how the tool was administered, the athletic population, and the defining criteria.11,21,39,40,45,50,213,215,226 There are many reasons for this wide range of those classified as disordered eaters. Many athletes consider disordered eating patterns normal and harmless. Others deny disordered eating patterns on standard questionnaires. Many studies referenced to assess the prevalence of eating disorders use questionnaires that assess symptoms of eating disorders without an assessment by a trained clinician or a screening tool that confirms defined disordered eating patterns.152 In 2004, the National Eating Disorder Screening program screened more than 16,000 students and 59% scored positive for symptoms of an eating disorder.50 Reinking et al239 determined that disordered eating patterns were not significantly different in athletes versus nonathletes in a collegiate setting. However, there was a greater disposition of disordered eating patterns in lean versus nonlean athletes.239 At least 1 confounding factor of this study was that there was a requirement at this university that all athletes take a nutrition class. Although some authors have shown that nutritional knowledge does change eating patterns in athletes,293,294 other studies question whether knowledge is easily translated into action in female athletes.238 Such studies remain valuable, but lead to a wide range of prevalence in research reports, as well as lack of consensus about the role of education on affecting eating behaviors.
There are several theories as to why disordered eating patterns occur, including incorrect popular perceptions, biologic factors, and psychological reasons. Many attribute the evolution of these unhealthy eating patterns to the overwhelming desire to be thin.9,11,19,21,245 Specifically with athletes, this desire is often held in conjunction with the desire to win at all costs.50 Many female athletes think and are told that “thinner is better.” There is a perception among athletes, coaches, and the media that thinner athletes are faster, stronger, and more powerful. Biologic imbalances in neurotransmitters (serotonin, norepinephrine, and melatonin) have been suggested as an etiology for eating disorders.39,40 Psychological contributing factors include poor coping skills leading to poor stress management, insufficient family support, sexual and/or physical abuse, and low self-esteem.40 Struggling with many changes in their bodies, adolescent female athletes are particularly at risk for development of disordered eating patterns that may be the stepping stone for the other components of the Triad. Early detection with knowledge of the warning signs of eating disorders is key (see Table 31-14).
Table 31-14Warning Signs of Eating Disorders11,17,21 ||Download (.pdf) Table 31-14 Warning Signs of Eating Disorders11,17,21
|Aneroxia Nervosa (AN) ||Bulimia Nervosa (BN) |
|Physical signs |
Significant weight loss unrelated to medical illness
Fat and muscle atrophy
Dry hair and skin
Cold, discolored hands and feet
Decreased body temperature
Decreased ability to concentrate
Lanugo (fine, baby hair)
|Physical signs |
Severe reduction in food intake
Excessive denial of hunger
Compulsive and/or excessive exercising without signs of fatigue or weakness
Peculiar, ritualistic patterns of food handling
Intense fear of weight gain
Exhibits much concern about weight
Eating patterns that alternate between purging and fasting
Depression, guilt, and/or shame especially following a binge
The spectrum of menstrual function is another component of the Triad and ranges from functional hypothalamic amenorrhea to eumenorrhea. Eumenorrhea is defined as regular menstrual cycles at intervals near the median interval for young adult women.213 In young adult women, menstrual cycles recur at a median interval of 28 days, which varies with a standard deviation of 7 days.213 Menstrual irregularities include primary amenorrhea, secondary amenorrhea, oligomenorrhea, and suppressed luteal phase (luteal phase deficiency) and anovulation.91,174 Amenorrhea is defined as the absence of menstrual bleeding and is classified as either primary or secondary. Primary amenorrhea refers to absence of menstrual bleeding by the age of 16 years even though other female sex characteristics are apparent or by age 14 years in the absence of sexual development. Secondary amenorrhea is defined as the cessation of the menstrual cycle for at least 3 months after the initiation of menstruation.50 Amenorrhea, as defined by the International Olympic Committee, means fewer than 2 menstrual cycles per year.3 The main difference between primary and secondary amenorrhea is that in the latter at least 1 menstrual cycle did occur, indicating that the reproductive chain, including the hypothalamus, pituitary gland, ovaries, and uterus, successfully completed at least 1 cycle.91,107,213 With secondary amenorrhea, this chain became disrupted and is not functioning normally.
The normal physiology of menstruation is a complex, coordinated interaction of hormonal and organ involvement occurring in a cyclical manner.11,50,109,121,251 The menstruation cycle is divided into 3 phases: the follicular phase, during which the egg matures; the ovulatory phase, during which the egg is released; and the luteal phase, in which the uterine lining prepares for the implantation of the fertilized ovum. If implantation does not occur, then the uterine lining is sloughed and menstrual bleeding begins.109,121 The hypothalamus produces and secretes gonadotropin-releasing hormone (GnRH) regularly. This stimulates the intact and functioning pituitary gland to produce luteinizing hormone and follicle-stimulating hormone. Luteinizing hormone and follicle-stimulating hormone stimulate the ovaries for maturation and release of oocytes (eggs). The ovaries cyclically produce estrogen and progesterone that stimulate the endometrium (uterine lining) to develop and the cyclical withdrawal of estrogen and progesterone result in menstrual shedding of the uterine lining. This ultimately leads to menstrual bleeding from a normal uterus with an unobstructed tract to the external genetalia.109,121 This well-coordinated, yet complicated, cycle of events may be disrupted anywhere along this process, demonstrating that there are many reasons for the onset of amenorrhea.109,121 Pregnancy and hypothalamic amenorrhea are the 2 most common reasons for the cessation of menstrual cycles. One subset of hypothalamic amenorrhea has been described as “exercise-related” or “athletic” amenorrhea.50,265 Determining the diagnosis of athletic amenorrhea is one of exclusion of all the other possible causes, requiring an extensive evaluation by a physician with experience and expertise with athletic women. It should be noted that cessation of menstruation is not a normal consequence of athletic participation or training for sport (see Table 31-15).174
Table 31-15Causes of Amenorrhea28,73
The loss of menstrual cycling coincident with exercise has long been recognized by professional dancers, athletes, coaches, and the medical profession.11,50 The etiology, prevalence, and treatment of athletic amenorrhea are not completely known and agreed upon to date. In the early 1970s, it was proposed that low body fat and weight were the cause of this cessation of menstrual bleeding. This hypothesis has since been refuted and other factors have been postulated and are currently under investigation. These factors include the physical stress of exercise, increased endogenous opioids from exercise, and overall energy availability based on the “energy balance” discussed previously.40,50,84,174,213 All of these factors are postulated to directly affect the production and release of GnRH from the hypothalamus.
The prevalence of amenorrhea again is difficult to accurately assess because some female athletes and coaches welcome the cessation of menstrual bleeding. This condition indicates to these athletes and coaches that sufficient training rather than a problem is occurring, so medical workup is not even considered. It is reported that 10% to 20% of vigorously exercising women are amenorrheic as compared to 5% of the general population when pregnant women are excluded.187 The prevalence of amenorrheic elite runners and professional ballet dancers rises as high as 40% to 50%.50,92,93,161,164,187,216 The dangers of prolonged amenorrhea include reversible loss of reproductive capacity and possibly irreversible bone loss. The long-term consequences of adolescent amenorrhea are yet to be fully understood and determined.
Oligomenorrhea is defined as menstrual cycles greater than 36 days or having less than 8 menses per year.95,213 This may result from anovulation, which results from low levels of both estrogen and progesterone or normal estrogen production but low levels of progesterone.213 Female athletes with luteal suppression often present with irregular menses. This component of the Triad still emphasizes amenorrhea, but an expanded view of the Triad includes all of these menstrual irregularities. Detection of menstrual irregularities are often attempted by interview or via a completed self-questionnaire by the female athlete. The preparticipation screening process is an ideal time to assess for these irregularities and appropriately refer to a medical expert such as a physician with experience and expertise with athletic women for a thorough evaluation.
The final component of the Triad is the BMD spectrum, ranging from osteoporosis to optimal bone health. Osteoporosis is currently the most common bone disease in the United States, affecting more than 25 million Americans to date.7,108,163,210 The definition per the Consensus Development Conference on Osteoporosis is a disease characterized by low bone mass, microarchitectural deterioration of bone tissue leading to enhanced skeletal fragility, and an increased risk for fracture.210 Measures of BMD with dual-energy X-ray absorptiometry (DEXA)26 are used to diagnose osteoporosis and osteopenia with diagnostic criteria that have been established for postmenopausal women.34 Figure 31-34 is a DEXA scan of a female athlete. Unfortunately, there are no similar diagnostic criteria that have been established for premenopausal women to date.155,210,215,225
DEXA Scan for individual with normal bone density
There are 2 types of bones: cortical bone, which is tightly compacted plates of bone, and trabecular or spongy bone, which is made up of bone spicules separated by spaces in a honeycomb fashion.70,93,95 The peripheral skeleton (long bones) is comprised predominantly of cortical bone. This bone is less susceptible to changes in reproductive hormones than the trabecular bone. The axial skeleton (pelvis, vertebral column, and ends of the long bones) is comprised mostly of trabecular bone. These aspects of our skeleton are more susceptible to changes in reproductive hormones reflecting the predominant location of bony changes that occur with both menopause and exercise-induced amenorrhea.70,215 BMD is determined by the ratio of osteoclastic (resorption) and osteoblastic (remodeling) activity. Weightbearing activities directly stimulate osteoblastic activity according to the Wolff law. Sex hormones, estrogen and testosterone, also favor osteoblastic activity with peak bone growth noted during puberty. The opposite effect of rapid bone loss is seen at menopause with the loss of estrogen. Estrogen also plays a role by limiting osteoclastic activity, thus improving the absorption of calcium at the gastrointestinal level and decreasing elimination of calcium at the renal level.70,95 Other factors affecting BMD include genetics, smoking, alcohol consumption, cortisol levels, and nutrition.34,36 Calcium and vitamin D consumption is critical for proper bone health. Calcium is necessary for bone remodeling, but the amount of calcium absorbed is dependent upon an adequate amount of vitamin D.23,104,108,217
Abnormalities in bone homeostasis have been documented in female athletes with both premature osteoporosis,72,108 scoliosis,45,108,282 and fractures, including premature osteoporotic84,91 and stress fractures of various locations 91,92,108,151 All athletes have cyclic stresses creating an increased rate of osteoclastic activity followed by osteoblastic activity. If adequate rest or time is not given, an imbalance preventing adequate new bone to be laid down occurs, resulting in a progressive weakening and fracture of the involved bone.108 This phenomenon occurs more frequently in female athletes, resulting in stress injuries to the bone. In a retrospective review of medical records of a Division I college institution over a 10-year period, Arendt et al23 demonstrated that female distance runners suffered the most stress injuries to bone (6.4%). Across all sports, female athletes were 2 times as likely to suffer stress injuries to bone as male athletes. The authors attributed this increased rate not only to sex-related factors but also BMD, menstrual history, and diet.113 Another study demonstrated that athletes with stress fractures had a lower bone density.203 Other studies have reported a higher incidence of stress fractures among amenorrheic and oligomenorrheic athletes than eumenorrheic athletes.23,189,216 Menstrual irregularities and decreased BMD certainly are not seen in every case of stress injury to bone, but both may place the athlete at higher risk.92
In addition to being at higher risk for stress injuries to bone, athletes with menstrual difficulties are unlikely to reach their total BMD potential resulting in an overall lower peak BMD and a decreased ability to maintain BMD over a lifetime because of lower levels of estrogen. Outcomes of studies regarding bone loss are pessimistic regarding the ability to reverse the lower BMD with treatment.93,113,189 There are studies that report an increase in serial BMD results with amenorrheic counterparts resuming menses, but the levels remain below their eumenorrheic-matched counterpart. Amenorrheic runners using hormone replacement therapy have demonstrated maintenance of BMD, but no gains.165 These studies collectively demonstrate the necessity to educate young female athletes in the importance of adequate nutrition, including calories, calcium and vitamin D intake, regular menses, and appropriate training levels, including weightbearing activities for their maturity level.
Interaction Between the Components of the Female Triad
The 3 components of the Triad have been presented and described as independent medical conditions, and now the link between them is detailed. The possible theories behind athletic amenorrhea were mentioned previously. The observations that both amenorrheic athletes had decreased body fat and individuals with AN had low body fat led to the hypothesis that altered body composition was not only correlated but causative. Loucks et al completed research matching amenorrheic and eumenorrheic (normal menstruation) athletes for body fat and found that menstruation status was independent of this variable.173 Another study concluded that the only difference between the groups (amenorrheic vs. eumenorrheic) with such matched athletes was the negative energy balance that occurred with training in the amenorrheic group.197 These studies indicate that it is the negative energy balance of caloric intake versus expenditure rather than body fat stores that is linked to the condition of amenorrhea.
Another theory to explain exercise-induced amenorrhea was that the physical stress of the exercise increased the levels of cortisol that were capable of disrupting the menstrual cycle. Again, both amenorrheic athletes and individuals diagnosed with AN demonstrated elevated cortisol levels with corresponding decreased levels of GnRH. As discussed previously in the section on amenorrhea, decreased levels of GnRH can result in exercise-induced amenorrhea. Cortisol has another role in the body as well with the regulation of plasma glucose and is released not only in response to physical stress of exercise but also with decreased levels of plasma glucose. The difficulty lies in separating these roles and determining whether high levels of cortisol disrupts the normal hormonal cascade by suppressing GnRH levels resulting in amenorrhea because of the physical stress of exercise or the decreased plasma levels of glucose. Loucks et al demonstrated that the hormonal cascade changes seen in luteinizing hormone could be normalized in females receiving dietary supplementation, highlighting once again the important role of nutrition (positive energy balance) with intense exercise.174
“Negative energy balance” as the cause of exercise-induced amenorrhea has been supported in the research.11,84,120 Two studies demonstrate that a combination of exercise training and caloric restriction in animals and humans results in amenorrhea with reversal upon an increase in caloric intake.174,197 This further supports the existence of a direct relationship between daily energy availability and the hormonal cascade controlling the menstrual cycle.1,2,173,174,197 These articles may explain why female athletes with similar body composition and training intensity have varied menstrual status including amenorrhea, oligomenorrhea, and eumenorrhea (normal menstrual cycling). It is not directly the exercise intensity that causes the change in the hormonal cascade controlling menstruation, but rather, the sustained negative energy balance in those female athletes not taking in enough calories for the energy expended during training. Interventions subsequently should include increased caloric intake in order to attain a positive energy balance in combination with other interventions to target restoration of normal bone metabolism. More specific intervention strategies will be discussed later in this chapter.
The interactions of the disordered eating patterns resulting in the negative energy balance and osteopenia should also be elaborated on. Unhealthy eating behaviors with diagnosed clinical eating disorders (AN, BN, EDNOS) and subclinical eating disorders can rapidly cause an inadequate intake of calcium, vitamin D, and vitamin K, resulting in decreased building blocks for osteoblastic activity to increase overall BMD and allow for normal bone homeostasis during sports participation. As discussed previously, the window of opportunity to reach peak bone mass occurs prior to the third decade of life and is most important in adolescence. These correspond with the same time that disordered eating patterns are most prevalent and the time that many female athletes are competing at high levels, with high training intensities, durations, and frequency. Failure to reach optimum BMD during this time secondary to inadequate nutrition may not be reversible.213
Additional interactions between menstrual irregularities and osteopenia are also evident. Some of these interactions with the multifactorial role of estrogen with normal bone metabolism and the ability to achieve peak BMD as it is related to secondary amenorrhea have already been discussed. The condition known as hypoestrogenemia lacks well-designed studies specifically addressing the effect of delaying menarche as a result of premenarchal training. Premenarchal training in a number of sports has been correlated with delayed menarche, but this does not imply causation.107,161 A retrospective study with college gymnasts suggests that delayed menarche is associated with increased risk of scoliosis, stress fractures, and low peak BMD.184 These patterns start to demonstrate the serious and long-term implications of triad interactions and the synergistic nature of the component spectrums. Each of the components of the Triad exist on a continuum of severity, thus the interactions between the components falls in a spectrum of severity as well. Early detection of the components greatly assists with the treatment of each component, as well as the interactions that may be present.
Preparticipation screenings provide an excellent opportunity to identify the components of the Triad. Appendices D and E are examples of screening questionnaires for information gathering regarding eating habits, menstrual history, and bone health. More extensive questionnaires and surveys regarding eating habits and menstrual history can be included should preliminary screening indicate a need. Additional resources can be found in Appendix F. Menstrual history is often used for predicting bone density.91,165 In addition, Drinkwater has demonstrated a linear relationship between the degree of bone loss and the degree of menstrual dysfunction.91,92 Any abnormalities with menstrual cycle detected in the medical history section should be noted and discussed with the primary care or team physician in order to facilitate further studies to confirm bone density. It has been recommended that any female athlete with history of clinical eating disorders, amenorrhea, or oligomenorrhea for more than 3 months have further study to determine bone density. Similarly, documented history of stress fractures may indicate further study. History of stress fractures, especially of the femoral neck, sacrum, or pelvis (cancellous bone), is increasingly concerning secondary to a recent study that found that female athletes with a stress fracture in cancellous bone are more likely to have osteopenia than athletes who sustain a stress fracture in cortical bone such as the tibia or metatarsal.164 Increasing access, ease, and affordability of DEXA scans have facilitated the ability to confirm a suspicion of bone density problems.
Logistically, implementing these screening tools works nicely in sports preparticipation screening. It is the experience of the authors and documented by other medical professionals that information regarding eating habits and beliefs, self-image, and menstrual history is more accurately gathered when there is a trained medical professional interviewing the female athlete rather than the use of tools that require self-administration.39,40,126 Many athletes with problems in these areas suffer guilt and shame regarding their behaviors and are skilled at hiding their actions, but most will provide honest and accurate answers to direct and nonjudgmental questioning. It is important to make clear that the information gathered will be held in confidence and will be used for the athlete’s benefit. Questionnaires such as found in Appendix D or a combination of established questionnaires (see Appendix E) may also be used outside the preparticipation screening environment for any female athlete suspected of having the Triad.