The Effect of Activating the Scapular Muscles During Warm-up on Shoulder Function and Baseball Pitching Performance in Male Adult Baseball Players: An Approach Using Electric Muscle Stimulation

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Background: Various warm-up exercises have been developed to improve baseball pitching performance and prevent throwing injuries. Although their effectiveness has been evaluated, their underlying mechanisms remain unclear. These mechanisms require elucidation to help develop more effective warm-up exercises for pitchers from different backgrounds. Many clinicians and team staff focus on optimal warm-up of the glenohumeral joint, which is a common site for throwing injuries; thus, it is important to expand the knowledge regarding developing the optimal warm-up. Purpose/Hypothesis: The purpose was to investigate the effects of scapular muscle activation during warm-up on shoulder joint function, pitching mechanics, and performance. The hypothesis behind activating the scapular muscles was that doing so would increase shoulder joint mobility and improve pitching mechanics and performance. Study Design: Controlled laboratory study. Methods: Fifteen male adult pitchers participated in this study. Two exercises were performed on the shoulder joint of the throwing side: the participant's usual warm-up (control) and activation of 2 scapular muscles (lower trapezius and infraspinatus) using electric muscle stimulation (EMS). Furthermore, EMS was set at 2 stimulation levels, resulting in 3 warm-up approaches. Joint mobility and pitch tests were performed immediately after each approach. These tests for each approach were repeated 3 times for each participant, with a washout period >7 days. Results: Of the 15 participants, 14 accomplished all tests. The EMS approach with stronger stimulation showed the following results as compared with the other 2 approaches: a significant increase in shoulder horizontal adduction in the passive mobility test and significant increases in shoulder-related kinematics, performance, and joint reaction force during pitching. Conclusion: Warm-up of the scapular muscles using EMS increased the shoulder joint function and yielded immediate improvement in pitching mechanics and performance. However, there was a potential risk of increased stress on the shoulder joint. Clinical Relevance: Although warm-up activating 2 scapular muscles may be important for achieving better pitching performance, this warm-up may also be needed to (1) provide a coordination exercise of the scapular muscles to stabilize the glenohumeral joint and (2) control the pitch count for restraining the risk related to throwing injuries.

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