Alterations in pitching biomechanics and performance with an increasing number of pitches in baseball pitchers: A narrative review.

In baseball pitchers, the association of fatigue with overuse injury and decline in pitching performance has been discussed frequently, but the scientific data concerning their interrelationships have been inconsistently reported. The purpose of this narrative review is to summarize and explore the evidence regarding acute changes in pitching biomechanics and performance from repetitive throwing motions among baseball pitchers. Muscle fatigue from repetitive throwing not only decreases muscle output but also disturbs the kinetic chain of baseball pitching. In addition, repetitive throwing can impair the proprioceptive and kinesthetic functions needed for accurate joint position sense in the shoulder and elbow. Consequently, these changes negatively affect ball velocity and pitching accuracy, two critical aspects of overall pitching performance. Moreover, the cumulative loading caused by fatigue contributes to the high prevalence of overuse injuries, particularly in the elbow and shoulder joints. Thus it is important to comprehensively understand the relationships among changed pitching mechanics, deteriorated performance, and musculoskeletal injury originating from muscle fatigue due to repetitive pitching.