Fast-Pitch Softball Players Use Biomechanical Compensations to Maintain Pitch Speed When Fatigued

PURPOSE: It is a common misconception that fast-pitch softball (FPS) pitchers experience fewer overuse injuries than baseball pitchers. In fact, the incidence density ratio of high school softball players to baseball players is 1.27, meaning that FPS players are injured more often than baseball players. FPS pitchers fatigue after approximately 100 pitches, commonly present with shoulder and lower back overuse injuries, and are at increased risk for lower-extremity overuse injuries. Yet, pitchers routinely throw 1,500–2,000 pitches in the course of a single weekend tournament. The purpose of this study was to explore the relationships between pitching, fatigue, and biomechanical compensations that may contribute to injury.

METHOD: Eight high school FPS pitchers, ages 15–18 yr, were studied in a prospective cohort design over the course of a simulated game. Pitchers were recruited from an FPS training academy in a metropolitan area. Pitchers had no history of sports-related surgery or current symptoms of injury. Outcomes were evaluated on the first and 125th pitch. Outcome areas included kinematics, pitch speed, strength, fatigue, and pain. Kinematics and pitch speed were assessed with an eight-camera video motion capture system. Thirty-six markers were placed on palpated bony landmarks to identify the thorax, pelvis, and upper and lower extremities in accordance with established standards. Joint positions were measured at push off, landing, and ball release of the pitch cycle. Strength was measured via dynamometry. Pitchers self-reported the Borg Rating of Perceived Exertion and a visual analog pain scale for measures of fatigue and pain, respectively. Paired t tests were used to detect changes in all outcomes. A correlation matrix was created to identify patterns in kinematic changes.

RESULTS: Ball speed did not change between Pitch 1 and Pitch 125 (p = .63), although Borg Rating of Perceived Exertion increased significantly (p = .01). Pitchers demonstrated significant strength reduction in shoulder internal and external rotation, flexion, scapular plane abduction, and in all three segments of the trapezius (p values = .001–.041). A nonsignificant decrease in elbow flexion strength was also noted (p = .062). Kinematic changes included an 8° decrease in pelvic lateral rotation at landing (p = .048), 11° decrease in elbow flexion at ball release (p = .027), and a nonsignificant 6° increased knee flexion at ball release (p = .072). Changes in elbow flexion correlated strongly with thorax lateral rotation (r = .717, p = .045) and pelvis lateral rotation (r = .830, p = .011) and negatively with pelvic tilt (r = –.774, p = .024) at ball release. All pitchers reported no pain throughout all trials.

DISCUSSION: These results confirm that elite FPS pitchers can maintain pitch speed despite measurable and self-reported fatigue while implementing biomechanical compensations. With their pitching arms fatigued, they use significantly less elbow flexion and altered pelvic mechanics to propel the ball at the same speed. These changes correlate with compensations throughout the kinematic chain. These results suggest that compensations can be elicited within the span of a typical FPS game. Further, they provide a missing mechanistic link between pitch mechanics and the incidence of chronic lower back and lower-extremity injuries among FPS pitchers.

IMPACT STATEMENT: The impact of this work is to highlight the injury risk associated with FPS pitchers performing to or past the point of fatigue. If these results can be replicated, high school and collegiate athletic associations would be well advised to limit the number of pitches thrown by FPS pitchers.