抄録
Introduction: The purpose of this study was to determine the electromyographic activities of the biceps during arm elevation in shoulders with rotator cuff tears and to clarify the relationships between the biceps activities and the isokinetic strength of the shoulder.
Methods: Forty shoulders were examined using a dynamic EMG: 18 shoulders with rotator cuff tears and 22 without tears (normal controls). The EMG activities during arm elevation were integrated and expressed as a percentage to the maximum voluntary contraction (% MVC). The isokinetic strengths of IR/ER and Abd/Add were measured in 28 shoulders (10 rotator cuff tears and 18 controls) using a CYBEX or a KIN-COM dynamometer.
Results: In the controls, the % MVC of the biceps was always less than 10% during elevation. Of the 18 shoulders with rotator cuff tears,6 shoulders showed increased activities of the biceps(p<0.05, highactivity group), whereas the remaining 12 shoulders showed 10 or 0 less-activities than the controls (low-activity group). Muscle strengths of the high-activity group, low-activity group, and the controls were compared. The high-activity group had the smallest strength and the controls the greatest. The difference between the high-activity group and the controls was significant(p<0.05).
Conclusion: The increased EMG activities of the biceps during arm elevation in rotator cuff tears with muscle weakness suggest that the biceps might act as a mover to compensate the shoulder weakness.
