Abstract
(1) Not all the rotator cuff muscles were active during the mover or synergist actions on the shoulder movements. Certain muscles came into use for specific shoulder movements. Supraspinatus performs an important function during abduction and is active as synergist during flexion and extension, but it is inactive during adduction, external rotation and internal rotation.
Infraspinatus performs an important function during external rotation and is active as a synergist during flexion, extension and abduction, but it is inactive during adduction and internal rotation. Subscapularis was the only muscle that was active during internal rotation without exertion during shoulder movements and was active as a synergist during other movements.
Teres minor porforms an important function during external rotation and extension, and was active as a synergist during flexion, abduction and adduction, and inactive during internal rotation.
(2) Deltoideus (pars clavicularis), pectoralis major, latissimus dorsi and coracobrachialis were inactive during internal rotation, and subscapuralis was the only muscle that was active during this movement without exertion.
(3) Infraspinatus and teres minor performs important function during external rotation, but deltoideus (pars spinata) was inactive during this movement.
(4) Teres minor was not always functioning the same as infraspinatus. Teres minor was particularly active during the latter half of abdunction and during adduction, but infraspinatus was active during abduction and inactive during adduction.
(5) Teres major was not always functioning the same as latissimus dorsi. Teres major was particularly active during extension and adduction, but latissimus dorsi was active during flexion, extension, abduction and adduction.
(6) It is believed that the active condition of the participating muscles differs in relation to the time taken to carry out a shoulder movement.
