BACKGROUND: High-intensity repetitive athletic activities may predispose the brachial plexus to repetitive stretch, compression, and subsequent injury, although painless shoulder weakness is a rare event. PURPOSE: The physical examination and electrodiagnostic findings in a series of United States Navy special warfare trainees who presented with acute painless shoulder weakness are presented, along with subsequent treatment and return-to-duty timeline. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: From August 2005 to August 2006, a total of 11 of 212 (5%) Navy Basic Underwater Demolition School trainees were identified with acute onset (<3 weeks) painless shoulder weakness without any prior shoulder injury. In all shoulders, symptoms began during a telephone pole lift-carry drill. All trainees underwent serial examinations, electrodiagnostic testing, and a comprehensive rehabilitation program. RESULTS: Physical examination revealed universal weakness in flexion and abduction and electrodiagnostic studies confirmed injury to the C5-6 area of the brachial plexus (axillary, suprascapular, and musculocutaneous). All 11 patients were removed from training and started on a physical therapy program until functional recovery at a mean of 21 weeks after onset of symptoms (range, 12-24). All 11 resumed military activities; however, only 6 completed the Navy Basic Underwater Demolition School program. CONCLUSION: In physically intense training or athletic environments, injuries to the upper brachial plexus may present with various forms of upper extremity dysfunction, including painless shoulder weakness. This information provides insight into a potentially debilitating shoulder problem and offers guidance on future training principles.
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