Applied anatomy and kinesiology, the mechanism of muscular movement . he exertion required to raise the arms to verticalposition and that stops many persons before they arrive. There isprobably some resistance to the last stages of the movement in theclavicular joints, and when the humerus strikes the acromion, if itdoes, that and the pull of the supraspinatus will resist furthermovement in the shoulder-joint; among the muscles, the rhomboid DEPRESSION OF THE ARM 105 and pectoralis minor passively resist the extreme upward rotationof the scapula, while the pectoralis major and latissimus resis
Applied anatomy and kinesiology, the mechanism of muscular movement . he exertion required to raise the arms to verticalposition and that stops many persons before they arrive. There isprobably some resistance to the last stages of the movement in theclavicular joints, and when the humerus strikes the acromion, if itdoes, that and the pull of the supraspinatus will resist furthermovement in the shoulder-joint; among the muscles, the rhomboid DEPRESSION OF THE ARM 105 and pectoralis minor passively resist the extreme upward rotationof the scapula, while the pectoralis major and latissimus resist theelevation of the humerus. Since the difficulty of holding the armfar enough back is so evident it would seem that the pectoral isthe greatest single factor in the resistance. DEPRESSION OF THE ARM. Normal depression of the arm, when there is no external resist-ance, offers no such difficulties as elevation. Not only does gravi-tation, when the trunk is erect, help instead of resist the movement,but the arm is brought down against the side with no joints, liga-. Fig. 59.—Depressors of the arm in action. P, pectoral; C, coracobrachialis;L, latissimus. ments, or muscles impeding its way. It is the exact reverse ofelevation and all the planes possible in elevation are also possiblein depression. The movements in the joints—depression of the humerus androtation downward of the scapula—appear to take place in the 106 MOVEMENTS OF THE SHOULDER-JOINT reverse order of elevation, the movement of the scapula occupyingthe middle half of the arm movement. A convenient way to study theaction of muscles in this move-ment is to have the subject depress the arms while he holds thehandles of an overhead pulley machine. The movement can betaken any desired speed and can be stopped at any level to noticechanges. When the arm is depressed in the sideward plane against theresistance of the pulley machine the pectoralis major, latissimus,and teres major can be felt in action through the en
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