Shoulder strength, power, and endurance in college tennis players

Twenty-four college tennis players were tested for bi lateral shoulder internal/external rotation strength on a Cybex 340 isokinetic dynamometer; they were posi tioned supine with the glenohumeral joint abducted to 90°. Subjects produced significantly (P < 0.01) more torque in internal rotation at 60 and 300 deg/sec in the dominant arm compared to the nondominant arm. Sub jects also produced significantly more power in internal rotation at 60 deg/sec in the dominant arm. No signifi cant differences between the dominant and nondomi nant arms were seen in internal rotation power at 300 deg/sec or in the internal rotation endurance ratio. No significant differences were seen in external rotation on any measurement. By significantly increasing the strength of the dominant shoulder in internal rotation without subsequent strengthening of the external ro tators, muscle imbalances may be created in the dom inant arm that could possibly affect the tennis player's predisposition to injuries caused by overloading of the shoulder joint. This study suggests that external rota tion strengthening exercises should be implemented in tennis conditioning programs to maintain muscle strength balance, and possibly reduce the chance of overload injury.