Why is the supraspinatus able to abduct the shoulder without additional muscular synergy?
What will be an ideal response?
ANS:
Mostly, the effectiveness of the supraspinatus lies in its rather large moment arm compared to the deltoid muscle. Although the supraspinatus has a small upward translatory component, this upward force can be offset by the downward pull of gravity on the humerus. If the force of the supraspinatus and gravity on the humerus are composed into a single resultant vector, the resultant force creates approximately equal rotation and downward translation of the humeral head. This makes the supraspinatus an effective, although not very forceful, abductor of the glenohumeral (GH) joint.
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