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Baseball is a sport enjoyed by athletes spanning a wide range of age and skill levels. The participants in this sport range from very young children playing in community-based programs to professionals at the major league level. The act of throwing demands that the athlete maximally accelerate and decelerate the arm over a short period of time, repetitively, and through extreme ranges of motion. At the same time, the thrower must maintain precise control of the ball being thrown.

There are nine field positions in the game of baseball. The infield positions are pitcher, first baseman, second baseman, shortstop, third baseman, and catcher. There are three outfielders located in right, center, and left field. While the overall dimensions of the field are variable, the distance between the bases and from the pitcher’s mound to home plate are standardized. The distance between each of the bases is 90 ft. The distance from the pitcher’s mound to the front edge of home plate is 60 ft 6 in.

Incidence of Injury

The NCAA Injury Surveillance Program for the 2009 to 2014 season reported an incidence injury rate of 6.8 per 1000 athlete exposures during competition and 3 per 1000 athlete exposures during practice.1 In American professional baseball, the incidence of injury has been reported at 3.61 per 1000 athlete ­exposures.2 The upper extremity is more at risk for injury than other parts of the body because of the extreme demands that throwing places on it. Pitchers demonstrated a 34% higher injury rate compared to other position players with upper extremity injury accounting for 51.4% of the incidents.2 In a prospective epidemiologic study, McFarland and Wasik reported a 19% injury rate over a 3-year period in Division I collegiate baseball teams.3 Of these injuries, 58% were to the upper extremity, 15% to the trunk/back, and 27% to the lower extremity.3 Upper extremity injuries accounted for 75% of the total time lost from the sport.3 It is essential that those working with baseball players have a thorough understanding of the mechanics of the sport to best prevent injury. When prevention fails, knowledge of the tissues at risk for injury will allow for early identification of injury so that the best treatment and rehabilitation programs can be implemented.

Biomechanics of Baseball


Throwing is a high demand activity that requires finely-tuned coordination, efficiency, and conditioning. For the pitcher, control is also of the utmost importance, and even subtle alterations in form can affect the thrower’s ability to locate the pitches successfully. Detection of these subtle alterations by the coach, athletic trainer, therapist, or physician can result in identification of the early stages of injury to the thrower.

Anatomic Considerations

Because the shoulder is the joint most vulnerable to ...

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