抄録
The purpose of this study was to clarify the role of the biceps brachii in the shoulder joint. Ten dominant shoulders of healthy men were studied. The average age was 21.5 yrs. The subjects were sitting and wearing an elbow brace locked in neutral forearm rotation. The peak torque was measured by a Kin-Com AP during isometric flexion and abduction of the shoulder. The electromyographic signals were recorded with surface electrodes from the LHB and the SHB with an NEC Multitelemeter System. The elbow was in 0°flexion and loaded with 30% MVC(peak torque), and EMG signals were collected at twelve different arm positions, which were arm flexion or abduction of 45°,90°and 135°in external or internal rotation. The elbow was then flexed of 90°. The signals were analyzed with respect to the IEMG. Each IEMG value was divided by the IEMG value of the MVC, which was expressed as %MVC. The signal levels increased for each externally rotated position in both heads at an increasing angle of flexion or abduction. The EMG level increased at external rotation in each elevated position. Higher activity was found in the LHB when the arm was medially rotated than in the SHB. Both heads of the biceps brachii are always active during an arm flexion or abduction. We suggest that the biceps brachii could act as a dynamic stabilizer of the humeral head.
