Chapter 19. Locomotion: Solid Surface

At the conclusion of this chapter, the student should be able to:

• 1. Identify and classify motor skills belonging in the categories that fall under the heading of moving one’s body on the ground or on another resistant surface.
• 2. Describe the anatomical and mechanical nature of motor skills representative of the major types of locomotor patterns.
• 3. Name and state anatomical and mechanical principles that apply to the locomotor patterns of walking, running, and jumping.
• 4. Evaluate performance of motor skills representative of the major locomotor patterns in terms of application of the related kinesiological principles.
• 5. Analyze the performance of someone performing a locomotor skill. Follow the kinesiological analysis outline presented in Chapter 1.

Locomotion is the act of moving from place to place by means of one’s own mechanisms or power. Locomotion in human beings is the result of the action of the body levers propelling the body. Ordinarily the propulsion is provided by the lower extremities, but it is occasionally provided by all four extremities, as in creeping, or by the upper extremities alone, as in walking on the hands or in suspension. It may involve the use of wheels, blades, skis, or other equipment attached to the feet, or it may involve a vehicle such as a bicycle or wheelchair, or a small craft such as a boat, canoe, or surfboard propelled by means of the arms or legs, with or without the use of a propelling implement such as oars, paddles, or poles. Locomotion may be on the ground or in the water but, at the present writing, not in the air without support. In all locomotion there must be a resistance against which the body part can push to generate a reaction force if motion is to occur.

All forms of locomotion performed on the ground constitute the category of motor skills of moving one’s body on the ground or on other resistant surfaces.

On Foot

• Walking
• Running
• Racewalking
• Climbing (inclined plane, stairs, ladder)
• Descending (inclined plane, stairs, ladder)
• Jumping, leaping, hurdling
• Skipping, hopping, sliding, sidestepping
• Dance steps
• Snowshoeing
• Stilt walking

On Wheels, Blades, and Runners

• Bicycling
• Skating and skateboarding
• Alpine and cross-country skiing and snowboarding
• Ice skating
• Wheelchair propulsion

On Hands and/or Knees or Hands and Feet

• Walking on hands
• Creeping and crawling
• Crutch walking
• Stunts

Rotary Locomotion

• Cartwheels
• Handsprings
• Rolls

To the casual observer, the movements involved in walking appear to be relatively simple, yet kinesiological analysis shows them to be exceedingly complex. The dovetailing of muscular action and the synchronization of joint movements beautifully illustrate the teamwork present in all bodily movements. Not even the most complex piece of machinery designed by the most skillful engineers exceeds the movements of the human machine in perfection of detail or in potential smoothness of function on a wide variety of terrain and in all conditions.

The work of Inman, Ralston, Steindler, Murray, and many others has served, over the course of the years, to emphasize the complexity of human walking (Rose and Gamble 1994). In the past, researchers have been limited to studying gait and trying to compensate for those factors that often limited people in walking. Currently, a great deal of work is being done in the area of functional electrical stimulation (FES). Using computers and electrical currents, it is now possible to program the muscles of the disabled patient in such a way as to artificially stimulate the muscles of the lower extremity to reproduce the action of walking. Depending on the state of the neuromuscular system, those who once were forced to rely on wheelchairs, braces, and canes are now starting to walk with the aid of such computerized systems.

Description

Walking is accomplished by the alternating action of the two lower extremities (Figure 19.1). It is an example of translatory motion of the body as a whole brought about by rotary motion of some of its parts. It is also an example of a periodic, or pendulumlike, movement in which the moving segment (in this case the lower extremity) may be said to start at zero, pass through its arc of motion, and fall to zero again at the end of each stroke. In walking, each lower extremity undergoes two phases: the swing or recovery phase and the support or stance phase. The support phase is further divided into heel-strike, foot-flat, midstance, heel-off, and toe-off phases. The toe-off phase of one leg overlaps the heel-strike and foot-flat phases of the other leg, thus producing a period of double support when both feet are on the ground. This double support phase is characteristic of the walk and serves to differentiate it from the run.

The kinematics of the walking gait are often described in terms of strides and steps. A stride is one full lower-extremity cycle. In walking and running, a stride is defined as being from heel strike on one leg to the next heel strike with the same leg. Stride length, then, is the distance covered during a single stride. A step starts with the heel strike on one leg and ends with the heel strike of the contralateral, or opposite, leg.

Gravity and momentum are the chief sources of motion for the swing phase; hence, this phase represents a ballistic type of movement, particularly when the individual is walking at a natural pace. The source of motion for the support phase is, for the first half, the momentum of the forward-moving trunk (provided by the propulsive action of the other leg) and, for the second half, the contraction of the extensor muscles of the supporting leg.

Anatomical Analysis

The six major components of walking have been defined as (1) pelvic rotation, (2) pelvic tilt, (3) knee flexion, (4) hip flexion, (5) knee and ankle interaction, and (6) lateral pelvic displacement. Each of these components is essential for efficient walking, and the loss of any one will cause an increase in the energy cost. Beyond the long-established six determinant theory, investigators have also developed the concept of dynamic optimization of gait. Dynamic optimization assumes that human walking is optimized to minimize energy consumption through the dynamic interaction of the complex kinetic link system (Vaughan 2003).

The action taking place in the joints of the lower extremity consists essentially of flexion and extension. But, in much the same way that the shoulder girdle cooperates with the arm movements of the upper extremity, the pelvic girdle cooperates in movements of the lower extremities. The pelvis has the double task of transmitting the weight of the body alternately first over one limb, then over the other, and of putting each acetabulum in a favorable position for the action of the corresponding femur. The adaptations of the pelvic position are made in the joints of the thoracic and lumbar spine as well as in the hip joints. Thus, as first one foot and then the other is put forward, the flexion and extension movements of the thigh are accompanied by slight rotary movements and abduction and adduction at the hips, and by slight lateral flexion and rotation of the spine (Figures 19.2 and 19.3).

The muscular analysis presented here is a compilation of results from numerous studies on the walking gait. Walking, both normal and pathological, is one of the most widely studied of all human movement patterns. Movement specialists would be well advised to keep abreast of the on-going research in the area of gait analysis. Because of the relative importance and complexity of the walking gait, a complete discussion of the muscular involvement in walking is presented.

Swing Phase

The swing phase begins with toe-off and ends with heel-strike.

Spine and Pelvis

• 1. Movements: Rotation of the pelvis toward the support leg and of the spine in the opposite direction; slight lateral tilt of the pelvis toward the unsupported leg. The simultaneous opposite actions help prevent excessive motion of the trunk. Pelvic rotation also lengthens the step and decreases the lateral deviation of the center of gravity of the body, whereas pelvic tilt decreases the elevation of the center of gravity.
• 2. Muscles: Semispinalis, rotatores, multifidus, and external oblique abdominal muscles on side toward which the pelvis rotates. Erector spinae and internal oblique abdominal muscles on opposite side. (Note: Rotation of the pelvis to the right constitutes rotation of the spine to the left. See Relationship of the Pelvis to the Trunk and Lower Extremities.) The psoas and quadratus lumborum help support the pelvis on the side of the swinging limb, and the gluteus medius and minimus on the support leg side support the pelvis against the pull of gravity.

Hip

• 1. Movements: Flexion; outward rotation (because of pelvic rotation); adduction at beginning and abduction at end of phase, especially if long stride is taken (also because of pelvic rotation, as well as stride length).
• 2. Muscles: The iliopsoas is the prime mover of the hip in the swing phase, with assistance from the rectus femoris, sartorius, gracilis, adductor longus, and pectineus, and the short head of the biceps femoris during the late part of the swing. The sartorius is active chiefly following toe-off.
• In the latter part of the swing phase there is no appreciable action of the hip flexors in normal walking on level ground. This is consistent with the ballistic nature of the movement. The hamstrings contract with moderate intensity during the knee extension part of the swing, and the gluteus maximus and medius contract slightly at the very end of the swing. The adductors longus and magnus, and presumably brevis, contract slightly after the swinging limb has passed the halfway mark. The function of the adductor magnus is not clear. It may help steady and guide the forward-swinging limb. In any event, its action is extremely slight, even in rapid walking.
• In rapid walking there is a noticeable increase in the activity of the sartorius and the rectus femoris and also a slight increase in that of the tensor fasciae latae.

Knee

• 1. Movements: Flexion during the first half; extension during the second half.
• 2. Muscles: As was true in hip flexion (and for the same reason), so also in knee flexion is there remarkably little muscular action in the swing phase of normal walking. The largest contributor to knee flexion during the swing phase is the flexion that is produced during toe-off as the knee extensors relax.
• The quadriceps extensors contract slightly at the end of this phase. The action of the sartorius, a two-joint muscle, has already been mentioned in connection with the hip. The action of these muscles, as well as that of the medial hamstrings, increases in rapid walking. In an easy gait the movement appears to be initiated by gravitational force and continued by momentum. This force is sufficient to extend the leg at the knee, except perhaps at the very end of the movement. In more vigorous walking the quadriceps femoris provides the force for leg extension.

Ankle and Foot

• 1. Movements: Dorsiflexion; prevention of plantar flexion.
• 2. Muscles: The tibialis anterior, extensor digitorum longus, extensor hallucis longus, and probably the peroneus tertius contract with slight to moderate intensity at the beginning of the swinging phase and taper off during the middle portion of this phase.
• Toward the end of the swing phase this group of muscles contracts again with considerable force in preparation for the heel-strike. The plantar flexors are completely relaxed throughout the entire swing phase.

Support Phase

The support phase begins with heel-strike and ends with toe-off. The portion between heel-strike of the forward foot and toe-off of the other—that is, the rear foot—constitutes a period of double support that is characteristic of walking but does not occur in running.

Spine and Pelvis

Rotation of pelvis toward same side and spine to opposite side: lateral tilt away from support leg.

The lumbar portion of the erector spinae contracts at heel-strike to stiffen the trunk for stability. There is also a low level of activity in the internal and external obliques, possibly to assist in trunk rotation in opposition to pelvic girdle rotation.

Hip

• 1. Movements: Extension through foot-flat to toe-off; reduction of outward rotation, followed by slight inward rotation; prevention of adduction of the thigh and dropping of pelvis to opposite side.
• 2. Muscles: During heel-strike the gluteal muscles and the hamstrings contract statically with moderate intensity. These contractions then taper off during foot-flat and disappear at midstance. A number of EMG researchers have found evidence of gluteus maximus activity in the early part of the support phase (Anderson and Pandy 2003; Kimmel and Schwartz 2006). The gluteus minimus continues to contract moderately during the middle portion. The only muscles of the hip that contract appreciably during the last part of the support phase are the adductors magnus, longus, and possibly brevis.
• In rapid walking the gluteus maximus and minimus contract with appreciable intensity during the first part of the support phase, and the adductor longus during the last part. The hamstrings apparently have but a small part in the supporting phase of normal walking. Only the long head of the biceps contracts at all, and it contracts only slightly at the very beginning of this phase. In rapid walking both the long head of the biceps and the semitendinosus contract with greater intensity during the first half of the support phase.

Knee

• 1. Movements: Slight flexion from heel-strike continuing into foot-flat, followed by extension from midstance until heel-lift when flexion for the swing phase begins. This flexion during the stance phase flattens the vertical path of the center of gravity of the body, thus increasing the efficiency of the gait.
• 2. Muscles: The quadriceps extensors contract moderately in the early part of the support phase, then gradually relax. They appear to control the slight flexion that occurs in the knee at the moment of heel-strike. The vastii continue to contract throughout the first half of this phase. As the leg reaches the vertical position, the knee apparently locks and makes contraction of the extensors unnecessary. The tension of the stretched hamstrings at the end of the swing phase, especially when a long stride has been taken, may well be the factor that initiates the slight flexion at heel-strike. In rapid walking all of these muscles contract more strongly and for a longer duration. There is an abrupt increase in their action in the second half of the support phase, which would seem to indicate that the extension of the leg at the knee is much more forceful in rapid walking than in normal walking.

Ankle and Foot

• 1. Movements: Slight plantar flexion, followed by slight dorsiflexion; prevention of further dorsiflexion, which the body weight tends to cause. Plantar flexion of ankle and hyperextension of metatarsophalangeal joints at the end of the propulsive phase, especially in vigorous walking.
• 2. Muscles: There is considerable action of the tibialis anterior in the early part of the supporting phase, especially at heel-strike. This action is likely related to the controlled lowering of the foot by eccentric contraction to prevent the foot from slapping down too hard. Contrary to earlier opinions, the tibialis anterior does not continue to show activity during the major weight-bearing period, but it becomes active again at toe-off. The extensor digitorum longus and hallucis longus follow a similar pattern. They reach their peak contraction almost at the moment of transition between the swing and support phases; they relax early in the support phase, commencing to contract slightly at the end of this phase.
  • The gastrocnemius and soleus become active from midstance to heel-off, contracting eccentrically to control ankle dorsiflexion as the center of gravity continues moving forward. Peak activity in the plantar flexors is reached from heel-off to toe-off as the foot pushes against the ground to initiate the next step.
  • The tibialis posterior is most active during the middle part of the support phase, one of its functions, according to Basmajian, being to prevent eversion (pronation) of the foot (Basmajian and DeLuca 1985). He points out that the peroneus longus and tibialis posterior apparently cooperate in stabilizing the leg and foot in weight bearing. The gastrocnemius and soleus act to decelerate the lower leg and stabilize the knee at midstance. There is a sharp increase in gastrocnemius and soleus activity beginning after the heel lifts and continuing until the opposite heel contacts the ground initiating the period of double support. Extension of the knee in the stance phase is always accompanied by calf muscle activity. In rapid walking, however, their activity is much more pronounced. The peroneus longus follows a simple pattern but does not seem to contract quite so strongly as the others, except in rapid walking. The peroneus brevis does not start to contract until about the middle of the support phase, but it contracts more strongly than the longus. In rapid walking it starts earlier and contracts with intensity soon after the halfway point has been reached.
  • The flexor digitorum longus contracts slightly during the middle portion of the support phase and increases abruptly to moderate contraction in the last portion. In rapid walking the contraction becomes strong. The flexor hallucis longus follows the same pattern, except that it does not start to contract until the middle of the phase.
  • The toe muscles, flexor hallucis longus, flexor digitorum longus, and the short, intrinsic flexors of the toes contract in response to the pressure of the ground against the toes. In the propulsive phase, especially in vigorous walking, this contraction is intensified. In all parts of the support phase the contraction of the toe flexors is greater in barefoot walking than when shoes are worn. This is especially noticeable when walking on turf or sand.

Action of Upper Extremities in Walking

Unless restrained, the arms tend to swing in opposition to the legs, the left arm swinging forward as the right leg swings forward and vice versa. This reflex action is usually accomplished without obvious muscular action and serves to balance the rotation of the pelvis. When the arm swing is prevented, the upper trunk tends to rotate in the same direction as the pelvis, causing a tense, awkward gait.

In early research, Murray and colleagues (1967) used the technique of interrupted light photography to investigate the action of the upper extremities in walking. They noted “patterns of sagittal rotation of the shoulder and elbow,” or flexion and extension of both joints. They found that, although the amplitudes of the arm swing pattern varied considerably from one subject to another, each individual had a similar pattern in all trials, even at higher speeds. Furthermore, they noted that the increased amplitude accompanying the faster speeds was due mainly to increased shoulder (hyper-) extension in the backward swing and increased elbow flexion in the forward swing. Maximum flexion of both the shoulder and elbow joints occurred at the moment of heel-strike of the opposite foot and maximum extension at the moment of heel-strike of the foot on the same side. These findings have been corroborated by later investigators, who have found a consistent “coupling” between actions of the lower and upper extremities during walking (Dietz et al. 2001; Li et al. 2001).

Although the arms appear to swing without muscular effort in walking at a normal pace on level ground, actually their pendular action was caused by a combination of muscular activity and gravity. The middle and posterior deltoid and the teres major were the muscles found to be most concerned, the latter two being active mainly during the backward swing. The posterior deltoid also contracted toward the end of the forward swing, leading one to suspect that it was serving as a brake to check the movement. The middle deltoid was found to be active during both flexion and extension of the arm at the shoulder joint. As this muscle is primarily an abductor, it seems that its function might be to keep the arms from brushing the sides of the body as they swing past it.

Neuromuscular Considerations

Walking is an action that relies heavily on reflex; little conscious control is necessary. On the contrary, if too much attention is focused on any part of the gait, tension is likely to develop and the natural rhythm and coordination are disturbed. Reflexes control not only the movements of the limbs but also the extension of both the supporting limb and the trunk in resisting the downward pull of gravity. This extension serves to give stability to the body in the support phases of locomotion, a stability that provides for effective muscular action in producing the necessary movements. Thus, in walking, as in all the motions of the body, smooth, coordinated movement requires properly functioning reflexes, normal flexibility of the joints, and optimum stability of the body as a whole in the weight-bearing phases of the act.

Two reflexes that play prominent roles are the stretch reflex and the extensor thrust reflex. The stretch reflex may be involved at the extremes in motion, particularly at the shoulder and in the lower extremity, assisting with the change in the direction of joint motion. The extensor thrust reflex may facilitate the extensor muscles of the lower extremity as the weight rides over the foot on the support leg.

Anatomical Principles in Walking

Several key anatomical factors affect the efficiency of the walking gait. Key factors to consider in any analysis of a walking pattern are the following:

• 1. Alignment
  • a. Good alignment of the lower extremities reduces friction in the joints and decreases the likelihood of strain and injury.
  • b. The stability of the weight-bearing limb and the balance of the trunk over this limb are important factors in the smoothness of the gait. Both are improved with good alignment of the weight-bearing segments.
• 2. Unnecessary lateral movements decrease gait economy. Lateral movements are usually due to excessive motion in the shoulders or pelvis.
  • a. Excessive trunk rotation may be caused by either exaggerated or restricted arm swing. Normally the arm swing exactly counterbalances the hip swing.
  • b. The pelvis may drop on one side if the gluteus medius is not contracted for support. The result is an exaggerated hip sway.
  • c. Pelvic rotation should be just enough to enable the leg to move straight forward. A straight sagittal plane action of the leg is ensured by keeping the knee and foot pointing straight forward in all phases of the gait. The feet should be placed in such a way that their inner borders fall approximately along a straight line. Deviation from this pattern of leg motion will produce a weaving, inefficient gait.
• 3. Normal flexibility of the joints (i.e., sufficiently long and flexible muscles, ligaments, and fasciae) reduces internal resistance and therefore reduces the amount of force required for walking.
  • a. The tendons of the two-joint muscles of the lower extremity contribute to the economy of muscular action in walking.
• 4. Properly functioning reflexes contribute to a well-coordinated, efficient gait. Injury, disease, or substance abuse can interfere with the walking reflex.

Mechanical Analysis

Walking is characterized by the translation of the body’s center of gravity forward as a result of the alternating pattern of the lower-extremity joint movements during the stance and swing phases. The forces that control walking are the external forces of weight, normal reaction, friction, air resistance, and internal muscular forces. The direction and interaction of these forces determine the nature of the gait.

The inertia of the stationary body is overcome by the horizontal component of the propulsive force. Because periodic movement is characterized by an alternating increase and decrease of speed, the inertia must be overcome at every step, and the greater the weight of the body, the greater is the inertia to be overcome. As the center of gravity moves forward, it momentarily passes beyond the anterior margin of the base of support and a temporary loss of balance results. At this point the downward pull of gravity threatens a complete loss of equilibrium. A timely recovery of balance is effected, however, as the foot is placed on the ground. Thus a new base of support is established and a new support phase is begun. The downward force of the body’s weight is counteracted by the vertical reactive force through the feet. If the vertical force exceeds that needed to balance the gravitational force at the time of push-off, an exaggerated lift to the body results, causing a gait characterized by a bounce or unusual spring.

When forward motion has been imparted to the trunk by means of the ground reaction to the backward thrust of the leg and foot, it tends to continue unless restrained by another force. Once the center of gravity passes beyond the base of support, it is essential to restrain the action of the trunk until a new base of support is established. Hence, as the foot is brought to the ground in front of the body at the close of the swing phase, a restraining, or loading, phase is constituted. This diminishes as the leg approaches midstance. During the period that the foot is in front of the center of gravity, there is a forward component of force in the thrust of the foot against the ground. This results in a backward, or braking, reactive force of the ground against the foot, which is transmitted to the leg and then to the trunk.

The degree to which the pressure of the foot actually imparts motion to the body in the propulsive phase and restrains it in the restraining phase is in direct proportion to the counterpressure of normal reactive force of the supporting surface. If the surface lacks solidity, as in the case of mud, soft snow, and sand, it offers too little resistance to give the needed counterpressure. The pressure of the foot results in slipping or sinking, and more pressure must be applied to achieve even a slow forward progress. Hence the efficiency of the gait depends on the right balance between the pressure of the foot and the counterpressure of the supporting surface (Figure 19.4).

Like counterpressure, friction is also an essential factor in the effective application of the forces needed in walking. Because of the diagonal thrust of the leg at the beginning and end of the support phase, friction between the foot and the ground is essential so that the counterpressure of the ground may be transmitted to the body. For efficient walking, friction must be sufficient to balance the horizontal component of force. If it is insufficient, the thrust of the foot results in a slipping of the foot itself rather than in the desired propulsion of the body. The greater the horizontal component of force (as when walking with a long stride), the greater the dependence on friction for efficient locomotion.

The forward-moving trunk meets with air resistance, which tends to push it backward. By inclining the body forward, the pull of gravity is utilized to balance the force of the air resistance. Under normal conditions this force is negligible and will not be noticed. When walking against a strong wind, it is necessary to incline the body farther forward to maintain balance. If the air resistance is not balanced by the force of gravity, it must be balanced by the contraction of the abdominal and other anterior muscles of the neck and trunk. If the body is inclined too far forward, however, the force of gravity acts too strongly on it and must be counteracted by tension of the posterior muscles. Thus the proper degree of forward inclination is a factor in muscular economy.

Mechanical Principles in Walking

A number of mechanical principles govern the walking gait. A mechanical analysis of walking should include all of these important principles.

• 1. A body at rest will remain at rest unless acted on by a force. The force for walking is ground reaction force produced by extension of the lower extremity against a resistive surface. Because walking is an alternating pendular motion of the lower extremities, the inertia of the body must be overcome at every step.
• 2. A body in motion will remain in motion until acted on by a force. Once motion is imparted to the trunk by the backward and downward thrust of the legs, the trunk has a tendency to continue in motion, even beyond the base of support. A brief restraining action of the forward limb serves as a brake on the momentum of the trunk.
• 3. Translatory movement of a lever is achieved by the repeated alternation of two rotary movements, the lever first turning about one end and then the other. In walking, the lower extremity alternates between rotating about the foot’s point of contact (support phase) and the hip joint (swing phase). When muscles act to stop or start rotation at one end of the lever, power may be transferred to or absorbed from other segments. This power flow is cyclic in walking (Zajac et al. 2003).
• 4. Force applied diagonally has both horizontal and vertical components. The vertical component of the ground reaction force used in walking serves to counteract the pull of gravity. The horizontal component of this force serves to (a) check forward motion of the trunk during heel-strike and (b) produce forward motion in the trunk during heel-off and toe-off.
• 5. The speed of walking is increased by increasing either the stride length or the stride rate, or both.
• 6. The speed of the gait is directly related to the magnitude of the pushing force and to the direction of its application. This force is provided by the extensor muscles of the lower extremity, and the direction of the force application is determined by the angle of the lower extremity when the force is being applied.
• 7. As propulsion of the body is brought about by the backward and downward push of the foot against the supporting surface, the efficiency of locomotion partially depends on the friction and ground reaction force provided by this surface.
• 8. The efficiency of gait is related to its timing with reference to the length of the limbs. The most efficient gait is one that is so timed as to permit pendular motion of the lower extremities.
• 9. Walking has been described as an alternating loss and recovery of balance (Steindler 1973). This being so, a new base of support must be established at every step.
• 10. Stability of the body is directly related to the size of the base of support. In walking, the lateral distance between the feet is a factor in maintaining lateral stability. Average step width is about 10 percent of leg length.

Walking Variations

Individual Variations in the Gait

Although the basic analysis of the gait is valid for all physically normal people, individual characteristics are present to such a degree that people are often recognized by their gaits. These variations may be either structural or functional in origin. The structural differences include unusual body proportions as well as differences in the limbs themselves, such as knock-knees and bowlegs. Extreme variations in the angle between the neck and the shaft of the femur and in the obliquity of the femoral shaft are also responsible for atypical gaits.

Variations in the forward-backward distribution of weight and in the length of stride have already been mentioned. Other variations in movement patterns that are not structural in origin are often related to characteristics of the personality. This fact was brought home forcefully to Wells when she attempted to help college students whose gaits were awkward. Almost invariably the students who walked the most awkwardly were those who were extremely shy or lacking in self-confidence. A study investigating the possible relationship between the two might be rewarding.

Pathological Gait

Pain, disease, injury, or congenital deformity have all been shown to produce deviations from a normal gait pattern. The possible gait adaptations are far too numerous to categorize in this text. Joint injuries such as sprained ankles or cruciate ligament repairs in the knee will undoubtedly be followed by an asymmetrical, limping gait. A stroke may interfere with the ability of the neuromuscular system to produce a normal gait pattern. Cerebral palsy, multiple sclerosis, Parkinson’s disease, and other neuromuscular conditions all produce gait variations that must be dealt with. It is important that the movement professional be well versed in the observation of gait patterns and offer any assistance required in the normalization of gait where possible. By recognizing deviations from a normal gait pattern, the student will be able to deduce the effects of gait variability and should be able to recommend appropriate remediation.

Age

Age is also a factor in gait variations. As the human body ages, there is some decrease in both strength and flexibility as tissues change. Balance often becomes a significant concern. As a result of these changes, the gait of the elderly is often modified from that of a healthy young adult. Typically, the gait of a more elderly person will have the same cadence as that of a younger person, but the step length will be shorter. Along with the shorter step length there tends to be a greater horizontal velocity component at heel-strike with a longer time for weight acceptance and motion of the center of gravity over the support foot. Step width tends to be slightly greater and is more variable. In addition, more time is spent in the double support phase, and propulsive force is reduced. These changes in the gait pattern, although producing a slower gait, produce greater stability (Lockhart et al. 2003; Owings and Grabiner 2004).

Obesity

Obesity has also been found to have an often negative effect on the walking gait. Obvious changes in gait would include increased impact forces in the foot-strike period, as well as a requirement for increased propulsive forces. Not as easily seen, but much riskier, are the increased medial and lateral forces that occur during walking in the obese person. These increased frontal plane forces lead to increased subtalar eversion. The combination of this eversion and the overall increase in force production may be linked to greater shear forces in the knee and increased deteroriation of soft tissue structures in that region. In addition, obese walkers tend to have a longer support phase and a shorter swing phase (McGraw et al. 2000).

Walking Up and Down Stairs, Ramps, and Hills

In walking upstairs or up a ramp, the reactive force resulting from the push of the legs should be directed through the body’s center of gravity and in line with the forward-upward slope. The most strain-free way of doing this is to incline the body forward in a straight line from the rear foot. The act of descending involves safely resisting the force of gravity on the body. The eccentric contraction of the muscles of the lower extremity enables the body to be lowered at a controlled rate, and maintaining the line of gravity toward the back of the base of support prevents forward falls (Figure 19.5). In walking upstairs or up a ramp or hill, the swing phase is characterized by an exaggerated knee lift and dorsiflexion of the ankle. According to Joseph and Watson, the hamstrings and tibialis anterior are the chief muscles involved (Basmajian and DeLuca 1985). In the support phase, when the action is chiefly extension of the knee and hip, with the ankle being either slightly plantar flexed or else maintained in the midposition on the ball of the foot, they found the chief muscular action to come from the gluteus maximus, hamstrings, quadriceps femoris, and soleus, with the gluteus medius helping maintain stability at the hip joint.

The swing phase of walking downstairs starts with a slight lifting of the rear foot to clear the step. This movement involves slight knee flexion and dorsiflexion of the ankle. It is followed by slight hip flexion, then hip and knee extension and plantar flexion of the ankle as the foot reaches for the step below the one the supporting foot is on.

The support phase starts with the ankle in plantar flexion and the knee in extension. As the foot assumes the body weight, the ankle, knee, and hip are approximately in their neutral positions with the knee very slightly flexed. As the other foot swings forward, the supporting leg engages in slight hip flexion, increasing knee flexion and dorsiflexion of the ankle. In the brief period of double support, the knee and ankle flexion reach their maximum. The main muscular action of the supporting limb, according to Joseph and Watson, consists of eccentric contraction of the hamstrings, quadriceps femoris, and soleus, with the gluteus medius contributing to hip stability as it does in ascending (Basmajian and DeLuca 1985).

Racewalking

The racewalking gait is an adaptation of walking intended to produce maximum walking speed without breaking into a run. Because the walk and the run are differentiated by the presence or absence of a double support phase, a racewalk must show a period of double support. A competitive racewalker attempts to minimize this double support period by increasing stride rate and decreasing stride length. In a normal walking gait, the stance phase accounts for 62 percent of the stride cycle and the swing phase makes up the other 38 percent. In the racewalk stance and swing phases, each accounts for 50 percent of the stride (Cairns et al. 1986). The peculiar straight-legged, hip swing appearance of the racewalk gait is produced by a further stipulation in competitive racewalking that requires that the knee of the support leg extend fully during the stance phase (Figure 19.6).

The racewalk gait differs from the normal walking gait in several ways. In racewalking there is greater ankle dorsiflexion just prior to heel-strike and the leg is already fully extended at the knee when this contact occurs. The feet follow a line of progression closer to the midline of the body than in normal walking. There is a more exaggerated arm swing and therefore greater trunk rotation. Because of the straight support leg, there is greater lateral pelvic tilt as the pelvis rises above the support leg and drops on the swing side. The combined motion of the hip, trunk, pelvis, and arms acts to compensate for the lack of knee flexion in the support leg, producing little vertical motion.

Description

Easy running, like walking, is a pendulum type of movement. It is doubtful, however, whether running at top speed can be so classified. The most notable factors differentiating the run from the walk are the period of double support, characteristic of the walk but not present in the run, and the period of no support (a “sailing-through-the-air period”), characteristic of the run but not present in the walk. In the run the foot hits the ground in front of the body’s center of gravity as in the walk, but not as far in front. As the speed of the run increases, the distance in front decreases until the foot contact is almost directly under the body’s center of gravity. This position reduces the restraining part of the support phase and gives greater emphasis to the propulsive part. At maximum speed, the restraining part disappears completely. The use of the term “driving phase” for the support phase in running indicates its propulsive nature.

Speed in running is the product of stride duration and stride length (v = d*t). Variation in either stride duration or stride length will change the velocity of the run. Although it might seem that simply increasing stride length would be an effective way to increase running speed, it is important to keep in mind the preceding discussion of restraining, or braking, force. As stride length is increasing forward, the restraining force will increase, an inefficient trade-off. In modifying running speed it is critical to maintain running efficiency.

The transition from running usually occurs at about 2 meters/second, with some variation. Investigators have found that just prior to this transition the propulsive force seems to diminish. No single distinct trigger for the transition from walk to run (or from run to walk) has been found, but it is generally agreed that one will move to a new gait when the effort required to maintain gait speed becomes too great (Neptune and Sasaki 2005; Prilutsky and Gregor 2001).

There are two major types of running. The first is the kind of running done for its own sake, as in competitive races or jogging. The major concerns here are time and distance in one direction. The second is the type of running that is part of games and sports. Here it is necessary also to consider matters such as change of direction or pace and stability. The technique for a run varies with the purpose, but the basic anatomical and mechanical aspects are the same, regardless of the purpose.

Anatomical Analysis

The difference between the joint actions in walking and running is a matter of degree and coordination. The joint actions are essentially the same, but the range of motion in running is generally greater. This is especially apparent in the actions of the swinging leg. The difference in coordination is evident in the period of nonsupport and the absence of the period of double support.

Swing Phase

The swing phase begins with toe-off and ends with the foot landing (Figure 19.7). It is more muscular than pendular and is longer than the support phase. In fast running the initial foot contact may be the ball of the foot and, in slow running, the heel or the whole foot. The flexed leg in the swing phase brings the mass of the leg close to the hip, reducing the moment of inertia and increasing the angular velocity of the forward-swinging thigh, which in turn drives the center of gravity of the body forward (Table 19.1).

Support Phase

The support phase begins with the contact of the forward foot and ends at toe-off when the body is driven into the air (Figure 19.7b to d). During this time the knee and ankle “give” in flexion and then extend as the body passes over the foot and is driven into the air. The support time decreases as the speed of the run increases (Table 19.2).

Mechanical Analysis

The speed of running is governed by the length of the stride and the frequency of the stride. Better runners have a greater stride length per given pace than poorer runners. The length of the stride is determined by the length of the leg, the range of motion in the hip, and the power of the leg extensors, which drive the entire body forward. Like any projectile, the distance the body will move once it is driven into the air depends on the angle of takeoff (distance that center of gravity is ahead of takeoff foot), the speed of the body’s projection, and the height of the center of gravity at takeoff and landing. The stride rate of the run is affected by the speed of muscle contraction and the skill of the performer.

In running, as in walking, the forces exerted to produce and control the movement are the internal muscular forces and the external forces of gravity, normal reaction, friction, and air resistance. There is no optimal speed in running because the energy needed to run is proportional to the square of the velocity. Therefore, whether the run is an easy jog or a full-speed sprint, economy of effort is a highly desirable objective. To achieve this it is essential that the runner observe the principles that apply to efficient running.

Mechanical Principles in Running

• 1. In accordance with the Law of Inertia, a body remains at rest unless acted on by a force. The force required to overcome inertia is greatest at takeoff and least after acceleration has ceased. The problem of overcoming inertia decreases as the speed increases.
• 2. In accordance with the Law of Acceleration, acceleration in the run is directly proportional to the force producing it. Hence, the greater the power of the leg drive, the greater the acceleration of the runner.
• 3. In accordance with the Law of Reaction, every action has an equal and opposite reaction. The force for the run is provided through the upward and forward ground reaction force in response to the downward, backward drive of the foot. The smaller the vertical component of this force, the greater the horizontal or driving component. In the most efficient run, vertical movements of the center of gravity are reduced to a minimum. There should be no bounce in running.
  • In an efficient run, the foot should strike the ground as close as possible to the line of gravity. If the foot should strike ahead of the line of gravity, the reaction force to this forward and downward thrust will be a backward and upward force, acting to retard forward motion.
• 4. The more completely the horizontal force is directed straight backward, the greater its contribution to the forward motion of the body. Lateral motions are inefficient and detract from forward propulsion.
  • The knees should be lifted directly upward and forward, with the motion of the entire lower extremity occurring within the sagittal plane. The arm swing should exactly counterbalance the twist of the pelvis and should not cause additional lateral motion.
• 5. Because a long lever develops greater speed at the distal end than does a short lever, the length of the leg in the driving phase should be as great as possible when speed is a consideration. Leg drive should be maximized as early as possible in the stance phase.
• 6. Resistance forces that are due to the moment of inertia of the free leg during the swing phase can be minimized. By flexing the free leg at the knee and carrying the heel high up under the hip, the leg is moved more rapidly as well as more economically. This high knee lift increases as speed increases.
• 7. The force of air resistance can be altered by shifting the center of gravity. A forward lean will work to counteract a head wind. A tailwind often enhances performance.

The Sprint Start

Because the object in sprint running is maximum horizontal velocity, sprint racers usually use the crouching start. This start enables the runner to exert maximum horizontal force at takeoff, providing maximum acceleration against inertia. In the sprint start the runner pushes against starting blocks fixed to the track surface. The blocks provide a surface against which the foot can push horizontally while utilizing maximum hip, knee, and ankle extension. Moving the rear foot farther back in the blocks can increase the push-off force but decreases the time to apply the force, which may result in a smaller impulse (Ft). During the acceleration phase of the race immediately after the start, the horizontal component of the leg drive gradually diminishes until a constant level of speed is maintained, during which period horizontal velocity remains uniform. The period of acceleration is characterized by a gradual decrease in the inclination of the trunk, a lengthening of the stride (made possible by raising the center of gravity as the trunk becomes more erect), and a decrease of the knee thrust, resulting from the gradual straightening of the knee at the moment of foot contact with the ground (Figure 19.8).

Jumping, hopping, and leaping are forms of locomotion familiar from earliest childhood, whether engaged in as a simple expression of joy and exuberance, as a self-testing and competitive activity, or as an integral part of a sport. In each instance the goal is to propel the body into the air with sufficient force to overcome gravity and in the direction to accomplish the desired height or horizontal distance. Like any projectile, the path of the body in the air is determined by the conditions at the instant of projection. The differences between a hop, jump, and leap relate to the landing and takeoff. In the hop, the same foot is used for the takeoff and landing. In the leap, the takeoff is from one foot and the landing on the other. A jumper takes off from one or both feet and lands on both feet. Each of these types of projection may be initiated from a stationary position (vertical jump, standing long jump) or preceded by some locomotor pattern such as running (running long jump, triple jump, high jump, hurdle).

The total horizontal distance covered by the performer of these related patterns is the sum of three distances: (1) the horizontal distance between the takeoff foot and the line of gravity of the performer, (2) the horizontal distance the center of gravity travels in the air, and (3) the horizontal distance the center of gravity is behind the body part that lands closest to the takeoff point. The total height may be considered to be divided into the distance between the ground and the line of gravity at the moment of takeoff and the maximum distance the center of gravity is projected vertically. For some activities, such as the high jump and the pole vault, the vertical distance between the center of gravity and the crossbar may be an additional important unit of distance.

All forms of these activities share the problems of adequate muscle strength to project the body against the force of gravity and the coordination needed for utilizing what might be called secondary motions for achieving maximum height or distance. The force that projects the body is provided by the forceful contraction of the extensor muscles of the hips, knees, and ankles and, to a lesser extent, by the arm flexor muscles in swinging the arms forward and upward.

Mechanical Principles in Jumping, Hopping, and Leaping

• 1. For movement to occur, inertia must be overcome. One of the chief problems in jumping from a stand is overcoming inertia. A preliminary motion such as swinging the arms and upper body backward and forward, taking a hop or a step, or using a preparatory run helps overcome inertia in jumping.
• 2. Muscles can store elastic energy. When concentric contraction is preceded by a phase of active stretching, elastic energy stored in the stretch phase is available for use in the contractile phase. Work done by the muscles that are shortening immediately after stretching is greater than that done by those shortening from a static state. For this reason the strong extension required for most jumping motions is usually preceded by a flexion phase. There should be no pause between this flexion and the thrust phase of the jump. This also makes full use of the phasic response of the stretch reflex.
• 3. Jumpers project themselves into the air by exerting force against the ground that is larger than the force supporting their weight. It is the reaction to the force that accelerates them upward. The faster and stronger the leg movements, the more force that is produced against the ground. Some of this downward force of the legs may itself be in reaction to upward motions of the upper extremities.
• 4. The upward thrust of the arms seen in the high jump accelerates the support leg downward, which in turn causes a reaction thrust from the ground. Trunk motion is also stabilized, allowing an increase in torque production at the knee. Additionally, the arm swing action in jumping has the effect of raising the center of gravity immediately prior to takeoff, which may result in increased jump height or distance (Ashby and Heegaard 2002; Feltner et al. 2004)
• 5. The magnitude of the impulse that the jumper exerts against the ground is a product of the forces and the time over which they act. The vertical impulses in all jumps are those resulting from the swinging actions of the arms and the extension of the hip, knee, and ankle joints. The magnitude of the forces depends on the strength of the muscle, speed of joint actions, and coordination of the joint movements. The time for generating vertical impulse is greatest in jumps from a stationary start and in those jumps that have maximum height as their goal. The time required for the generation of impulse can also vary with the jumping style. In the high jump, for instance, the Fosbury flop style generally has shorter takeoff times than the straddle. Those jump styles with shorter takeoff times have generally produced higher jumps, apparently maximizing force production to produce a greater vertical impulse in less time.
• 6. The path of motion of a body’s center of gravity in space is determined by the angle at which it is projected, speed of projection, height of the center of gravity at takeoff, and air resistance. The angle of projection varies depending on the purpose of the jump. In the long jump, where the goal is maximum horizontal distance, the optimum angle of projection is between 20 and 26 degrees. This angle is governed by the speed of the preparatory run and the vertical velocity generated at takeoff. The majority of the takeoff velocity is horizontal. Jumping at a 45-degree angle would require equal horizontal and vertical velocities. Because run velocities in the long jump are fairly fast, it would take a very large impulse to generate an equal vertical velocity. The long jump takeoff is too quick to allow for generation of this vertical impulse. Slowing the takeoff to the point where generation of equal velocities are possible would result in such low horizontal velocities that most of the jump distance would be lost. The most commonly quoted proportion between horizontal and vertical velocities is 2:1.
  • In the high jump the angle of projection is much greater. At the moment of takeoff the center of gravity should be as high as possible and the vertical velocity should be maximum. In the running high jump, some horizontal velocity is necessary at takeoff to carry the performer forward over the bar.
• 7. Angular momentum may be developed by the sudden checking of linear motion or by an eccentric thrust (Figure 19.9).

Wheels, Blades, and Runners

Often, human locomotion over resistive surfaces is accomplished using the mechanical aids of wheels, blades, or runners. Devices such as bicycles, various types of roller skates, skis, and ice skates are designed to allow human beings to move farther faster for less effort, or to enable them to move quickly and easily over otherwise difficult surfaces. Unlike friction in locomotion involving a body segment in contact with dry, firm ground, friction using wheels, blades, and runners must usually be minimized in some respect rather than maximized. In using wheels for human-powered locomotion, friction in axles and rolling friction between wheels and ground must be kept to a minimum to avoid the heat and wear caused by excessive friction. With runners and blades, reducing friction between the mechanical device and the ice or snow surface is the primary concern.

The most common form of human-powered locomotion, the bicycle, is also one of the most efficient in terms of transferring human muscle power to motion. Because the rider is constantly positioned over the center of gravity of the machine, the cycling motion has no braking or retarding phase. The continuous cyclic motion coupled with pedal and gear systems working on the principles of wheel and axles provide a mechanism in which little kinetic energy is wasted (Figure 19.10).

The speed at which the bicycle travels is determined by the gear ratio at which the bike is being operated, the pedal cadence of the rider, and the slope. The gear ratio of the bicycle determines the distance that can be traveled in each pedal revolution. A bicycle in first gear (smallest rear gear) need undergo only a single pedal revolution to cover the same distance as ten pedal revolutions in tenth gear, but it requires much greater force because of the shortened force arm in the wheel and axle configuration. On flat ground an efficient cyclist will use a small rear gear and forceful strokes to move the bike quickly. As the slope of the route increases, the cyclist will increase the size of the rear gear used, which will have the effect of maintaining the sense of effort at a relatively constant level but will decrease bicycle speed.

The force that produces pedal revolutions is provided by a cyclic extension–flexion motion of the lower extremities. The magnitude of the force that must be exerted depends on the gear ratio chosen. A lower gear, with a smaller force arm, requires greater pedal force but produces a greater distance traveled for each pedal revolution than do the higher gears with larger force arms. The pedal cycle itself has an extension, or power, phase and a flexion, or recovery, phase. Starting with the foot at the top of the pedal circle (top dead center, or TDC) and moving through the first 90 degrees of extension, the active muscles are the gluteus maximus, the rectus femoris, and the soleus, with the three vasti becoming active slightly before the rectus femoris. From 90 degrees to 180 degrees the hamstring group and the gastrocnemius become active. From 180 degrees back to TDC, muscle activity is primarily in the tibialis anterior with coactivation of the rectus femoris (Clarys and Cabri 1993; Neptune and Herzog 2000).

Although bicycling is an efficient form of locomotion when the system is in motion, kinetic energy is lost in stopping and starting. Each time the bicycle comes to a stop, kinetic energy is transferred to the braking system. To start the bicycle in motion, inertia must be overcome and kinetic energy reestablished. Along with inertia, rolling friction must constantly be overcome. This friction is inversely related to wheel diameter, which is why bicycles are more efficient than many other wheeled objects such as skateboards and roller skates. Rolling friction is greatest at the beginning of motion. As the wheel velocity increases, rolling friction decreases.

Increased velocity in bicycling produces increased air resistance acting against the cyclist. Drag increases as flow velocity increases. Often the cyclist will adjust the body position in an effort to reduce drag. The low handlebar position common in most racing and touring bicycles is an attempt to streamline the body, to reduce the surface area against which drag may act.

In most other forms of human-powered locomotion involving wheels, the movement involved is cyclic but not continuous as it may be in bicycling. In roller skating and in-line skating, for example, force is produced by each leg in turn, with a period of glide occurring between strokes. During this period of glide, there is a loss of velocity from friction. This means that some of the force expended on every stroke is used to regain lost velocity. Skateboards are similar but usually rely on only one leg for propulsion, the other leg maintaining constant contact with the moving board.

Both roller skates (or in-line skates) and skateboards are highly efficient during downhill motion. Velocity increases continuously because of gravity with no effort on the part of the human rider. Most will quickly remember, however, that in order to go down there must at some point have been an equivalent effort in the upward direction.

In ice skating, there is very little friction between the skate blades and the ice. This friction is reduced even further by a slight melting of the ice resulting from the pressure of the blade. Because of this extremely low coefficient of friction, it is not possible to push off in a backward direction as in running or walking. Instead the skate blade is turned perpendicular to the direction of glide. The same pressure that produces the slight melting of the ice also causes the blade to sink slightly into the ice, allowing the blade to thrust against the ice as force is applied. Thus the slight depression in the ice provides the equal and opposite reaction necessary for forward motion (Figure 19.11). Besides the lateral push-off, ice skating differs from running in that little plantar flexion occurs in the push-off. Plantar flexion at this point of the skate stroke will probably scrape the skate toe along the ice, increasing friction.

As in other forms of human locomotion, speed in ice skating is based on stride length and stride rate. As velocity increases, the body also inclines forward to a greater degree and the feet separate. In speed skating the trunk may be inclined forward to a horizontal position to reduce drag. In figure skating, ice hockey, and recreational skating, this degree of lean is less common (Figure 19.12).

Similar to ice skating but using runners instead of blades is the sport of skiing. At present there are two basic forms of skiing: nordic, or cross-country, and alpine, or downhill. In addition several other forms of sliding on snow are gaining in popularity and exposure. Ski jumping combines the speed of downhill skiing with aerodynamics and landing skills. Freestyle skiing uses the vertical velocity provided by small jumps or bumps to give the skier enough time in the air to perform a variety of gymnastic-style moves. Snowboarding replaces the familiar two skis with a single snowboard, closely related to surfing and skateboarding.

Cross-country skiing is most closely related to walking, running, and ice skating in that an alternating stride pattern is frequently used for propulsion. The most common stride pattern in cross-country skiing is the diagonal stride, in which a backward thrust with one ski produces a forward glide on the forward or gliding ski. Ski poles are used to add additional thrust (Figure 19.13).

More recently, competitive skiers have been using a marathon skate stride or a V-skate stride. In both skating strides, the thrust is lateral, as in ice skating, rather than straight back. The marathon skate stride in cross-country skiing uses a single leg thrust, whereas the V-skate stride uses an alternating stride pattern. In both skate strides, the push from the rear ski is at a 30-degree angle to the glide direction.

Alpine or downhill skiing relies primarily on gravity for a propulsive force. The skier starts at the top of a slope (usually through mechanical transportation) and glides to the bottom. The movement problems encountered by the alpine skier revolve around changing directions and maintaining balance at high speeds while undergoing a variety of horizontal and vertical disturbances. In competitive alpine skiing, speeds are such that air resistance also plays a major role. The low crouch position assumed by most alpine racers reduces the surface area and thereby reduces form drag (Figure 19.14).

Rotary Locomotion

In general, the factors responsible for the successful performance of rotary locomotion are the magnitude, direction, and accurate timing of the forces contributing to the desired movement of the body, including the advantageous use of the force of gravity whenever possible.

The most common activities in this category are forward, backward, and sideward rolls, cartwheels, and handsprings. Each of these is achieved by rotating about the body’s successive areas of contact with the supporting surface. In forward rolls, for instance, the body rotates about the hands, shoulders, rounded back, buttocks, and feet (Figure 19.15) and in cartwheels, about each hand followed by each foot with the body rotating laterally in a fully extended position. The impetus for the forward roll is given by the hands and feet, the direction of their thrust being a combination of backward and downward: backward to send the body forward, and downward to resist the downward pull of gravitational force on the head and trunk. When the hands and feet are no longer pushing, the head is tucked forward and the back is rounded with the knees bent close against the body to facilitate the roll. During the foot thrust, the hips are high, both for ensuring a stronger backward thrust with the legs and for making greater use of the force of gravity for the roll over the back.

Because a body at rest will remain at rest unless acted on by a force and a body in motion will continue in motion unless acted on by a force, it is important to keep the body moving in successive rolls and not let it come to a momentary halt following each roll. Even the briefest of interruptions necessitates overcoming inertia after each revolution. It takes velocity to acquire sufficient momentum to prevent these halts; therefore, each backward thrust of hands and feet against the ground should be as forceful as possible. Rotary movement is accelerated by shortening the radius. In both forward and backward rolls the radius is shortened by tucking the flexed lower extremities close to the body when the back is in contact with the floor.

Locomotion by Specialized Steps and Jumps

Other forms of ground-supported locomotion not involving the use of special equipment include two general categories. One of these consists of acrobatic stunts and athletic events, such as walking on the hands, successive jumping, and hurdling either with or without actual hurdles. The other category consists of activities used both in children’s play and in forms of dance. It includes skipping, hopping, galloping, sliding, sidestepping, leaping, and standard dance steps, such as the polka and mazurka.

• 1. Try this as a class exercise, working in pairs. A stands with heels against a wall with the feet otherwise in a comfortable, “natural” position in readiness to walk. B holds a ruler across the toes of A’s feet and draws a line against the ruler. A then stands with feet parallel at right angles to the wall, and again B draws a line. Measure the distance between the two lines. This measurement is likely to vary from 0.5 cm to 2.5 cm in a sizable class. A and B now change places and repeat.
  • Assume that you are to engage in a walking race of 1000 meters; also assume that if you toed straight ahead, each step would be 1 meter long. It would therefore take you 1000 steps to cover the distance. But suppose you toed out so that each step was (your measurement) _________ short. How many meters short of the finish line would you be when you had taken 1000 steps? (Answer: If the distance between the two lines had been 0.4 cm, you would be 0.4 × 1000 = 400 cm, or 4 meters, short.)
  • Implication: If you are walking against an opponent who walks at the same rate as you, but who toes straight ahead, you would be 4 meters behind when you cross the finish line. Yet, presumably you took the same number of steps.
• 2. Observe the gait of people on the street or campus, detect individual characteristics, and analyze them using anatomical and mechanical principles.
• 3. Get a subject to walk in each of the following ways. Observe and note differences in the movements of the head, shoulders, hips, and so forth.
  • a. Place one foot directly in front of the other.
  • b. Keep a lateral distance of 20 to 25 cm between the feet.
  • c. Point the toes out.
  • d. Point the toes in.
  • e. Point the toes straight ahead.
  • f. Take a short stride.
  • g. Take a long stride.
• 4. Select four or five individuals who differ in leg length. Get them to practice walking until each one finds the stride and speed that feels most comfortable. Compare their strides and measure the distance between footprints for each individual.
• 5. Observe several individuals as they run. Look for the application of the principles listed. Which are “violated” and how?
• 6. Using the iliac crest as an estimate of the center of gravity, trace the path of the center of gravity on a sequence drawing of some form of jump (see Figure 14.21). Determine the percentage of the distance jumped that can be attributed to each of the following:
  • a. Distancecenter of gravity is in front of takeoff point at the moment of takeoff.
  • b. Distance center of gravity travels while body is unsupported.
  • c. Distance center of gravity is behind landing point.
• 7. Compare the segment positions at several points during the execution of a standing long jump or vertical jump as done by several “poor” jumpers and several “good” jumpers. Identify the principles of concern in these jumps. Evaluate the performance by stating the related principles. On the basis of this information, try to improve the performance of the “poor” jumpers.
• 8. Choose a locomotor pattern not discussed in this chapter (hurdling, for example). Perform a complete kinesiological analysis, taking particular note of the purpose of the motion, its classification, and the nature of the motion. Include also muscle participation, neuromuscular considerations, and mechanical factors. Identify those principles that will help you determine whether someone performing this pattern is doing it correctly. Conclude the analysis with a prescription for improvement, including suggested methods for change and the elimination of violations of principles.