Electromyographic Activity of Shoulder Muscle at Different Positions During External Rotation / 体力科学

Electromyographic activity of the shoulder muscle at 20 and 90°abduction (20 Abd, 90 Abd) during external rotation was investigated in seven healthy men with no history of injury or instability of the shoulder joint.<BR>Electromyography (EMG) was recorded using intramuscular fine-wire electrodes inserted into the M. Supraspinatus, M. Infraspinatus and M. Teres minor, and with bipolar surface electrodes on the middle and posterior parts of M. Deltoid anti the upper and middle parts of M. Trapezius. To compare activity in different muscles, the integrated EMG (iEMG ) activity of each muscle was normalized.<BR>M. Infraspinatus and M. Teres minor showed significantly higher activity at both the 20 Abd and 90Abd compared with the middle and posterior parts of M. Deltoid and upper parts of M. Trapezius. M. Supraspinatus, the middle and posterior parts of M. Deltoid, and upper and middle parts of M. Trapezius all showed a difference in activity level between the two positions.<BR>These findings suggest that when M. Infraspinatus and M. Teres minor contribute to external rotation as a stabilizer and prime mover, consecutively, M. Supraspinatus, the middle and posterior parts of M. Deltoid, and upper and middle parts of M. Trapezius function according to the positions. Moreover, the activity of the upper and middle parts of M. Trapezius in 90Abd should influence stabilization, adduction and upward rotation of the scapula. Therefore, we conclude that the external rotation position is closely related to shoulder muscle activity and coordination.

Electromyographic analysis of shoulder muscles during shoulder external rotation with reference to load magnitude / 体力科学

Electromyographic muscle activities of the shoulder muscles during shoulder external rotation with reference to load magnitude were studied in 8 healthy male subjects without history of shoulder injuries. In addition, we discussed the relationship between rotator cuff muscles and superficial muscles. The subjects performed shoulder external rotation from 60°internal rotation to 45° external rotation at 20° of shoulder abduction and 20° of flexion. A Cybex dynamometer used to prescribe angle and velocity of the shoulder movement. At the same time, intramuscular wire electrodes were inserted into the supraspinous, infraspinous and teres minor muscles, and then surface electrodes were placed over the posterior deltoid and middle trapezius muscles. The load magnitude ranged 2-18 Nm and the angle velocity was set at 15 deg/sec. The rotator cuff muscles became significantly to be activated from 2 Nm (the supraspinous and infraspinous m.) and from 4-5 Nm (the teres minor m.) compared with the muscle activity during non-load. The superficial muscles became significantly to be activated from 4-7 Nm (the posterior deltoid m.) and from 3-6 Nm (the middle trapezius m.) compared with the muscle activity during non-load. Within the load range (18 Nm 46.8% MVC), %iEMG of the rotator cuff muscles was always larger than that of the superficial muscles. Therefore, we concluded that the contribution of the rotator cuff muscles was larger than that of the superficial muscles up to 3-4 Nm, and activities of the superficial muscles increased gradually from 3-4 Nm during shoulder external rotation.