Throwing shoulder in baseball pitchers
Authors:   , Leenen Antonius Joannes Renier 
Published: July 2024

Baseball pitchers play a crucial defensive role, significantly influencing game outcomes. The high velocity and precision required in pitching place immense stress on the shoulder, leading to a high incidence of injuries. Professional pitchers often sustain injuries due to the repetitive and high-load nature of pitching. This dissertation aims to advance knowledge about the mechanical load and injury risk of the throwing shoulder in baseball pitchers by studying the kinetic chain, the function of the pectoralis major, and the relationship between nociceptive pain and movement behavior.

The prevalence and characteristics of musculoskeletal symptoms in talented Dutch pitchers were explored over two competitive seasons. Shoulder and elbow symptoms were most common, followed by lower back symptoms, and were associated with decreased functional status. A questionnaire addressing these joints’ unique demands was developed and adapted into Dutch, demonstrating good reliability and validity.

A subsequent study examined the throwing shoulder through the biomechanical concept of the kinetic chain to better understand the pitching motion. Optimal kinetic chain functioning is believed to enhance performance and reduce injury risk. The study assessed the impact of impeded mobility within and between the pelvis and trunk segments, crucial for generating kinetic energy. Mobility impediments resulted in decreased performance, yet joint power and mechanical loading of the shoulder and elbow remained unaffected. Contrary to expectations, compensatory adjustments at the end segments of the kinetic chain did not emerge in response to the mobility impediment. Instead, compensation occurred earlier in the kinetic chain, affecting the separation time between the pelvis and trunk and the pelvis angular velocity.

The pectoralis major role during fastball pitching was examined. The study questioned whether the pectoralis major actively and passively generates force to optimally position the throwing arm during the late cocking and early acceleration phases. Activation of the pectoralis major was observed before maximal horizontal abduction of the arm, indicating active force generation. Simultaneously, the relative muscle lengths increased beyond optimal length, suggesting passive force generation through eccentric contractions. This evidence indicates that the pectoralis major plays a crucial role in optimally positioning the throwing arm and potentially preventing scapulothoracic hyperangulation.

The relationship between nociceptive shoulder pain and movement behavior was investigated. The study examined the extent to which immediate nociceptive pain relief affects the maximal angular contributions of the shoulder girdle and trunk during a semi-constrained reaching task in patients with persistent shoulder pain. Findings indicate that nociceptive pain does not significantly alter shoulder and trunk kinematics during overhead reaching tasks, even with acute pain relief. This insight enhances the understanding of the interplay between pain and movement behavior, critical for pitching biomechanics and injury management.

The dissertation concludes with a general discussion synthesizing the main findings and conclusions. This synthesis includes a critical discussion of research limitations and explores practical implications. The study advances understanding of mechanical load and injury risk in pitchers’ throwing shoulders by exploring biomechanical principles beyond the kinetic chain. While the kinetic chain principle adhering to the summation of speed principle can explain pitching, the principle of optimal coordination of partial momenta is also valuable. These principles may coexist in pitching performance. The catch-up theory, built on the kinetic chain principle, is not applicable to pitching. The pectoralis major muscle functions eccentrically, optimizing arm positioning to enhance performance without increasing injury risk. Persistent nociceptive pain is not directly related to movement strategies, suggesting rehabilitation should focus on broader strategies beyond pain alleviation. Monitoring early symptoms and technique alterations is essential for preventing overuse injuries and improving pitching performance. A prospective cohort study is recommended to examine the relationship between early symptoms, technique alterations, and injuries.