No report in the English literature exists on objective muscle testing following the Mumford procedure (distal clavicular resection). Twenty-three athletes, including six at the professional level, were evaluated an average 3.7 years after the Mumford procedure was performed for degenerative changes after a Grade I or Grade II dislocation. All athletes were evaluated with an in depth questionnaire, physical examination, and radiographic study. Seventeen performed Cybex testing of both shoulders. All but one were satisfied with the surgery. Sixteen returned to their same level of sports activity, including five of the six professional athletes. The most common complaint of all those not achieving the previous level of sports was the inability to achieve their previous maximum bench press strength. All athletes demonstrated full motion; five exhibited painless crepitation at the acromioclavicular joint. Ten of the twenty-three exhibited increased horizontal clavicular motion. Radiographs demonstrated an average of 1.9 cm of bone resection, with varying amounts of ossification present between the remaining clavicle and acromion in eight athletes. The involved limb performed significantly more work than the sound limb in flexion (P = 0.0133) and internal rotation (P = 0.0575) at 300 deg/sec. The involved limb performed significantly more repetitions at 300 deg/sec than the sound limb in the extension plane (P = 0.0373). The sound limb was significantly stronger during extension (P = 0.0759) and flexion (P = 0.0063) at 60 deg/sec compared to the involved limb. The sound limb performed significantly more total repetitions at 300 deg/sec in the abduction-abduction plane than the involved limb (P = 0.0843).(ABSTRACT TRUNCATED AT 250 WORDS)