The subacromial bursa is a sac-like fluid-filled structure that facilitates the gliding of the rotator cuff under the acromion. Impingement involves compression of the subacromial bursa between the greater tuberosity of the humerus and the acromion. This can result in shoulder pain.
Contracting the infraspinatus externally rotates the humerus and draws the greater tuberosity away from the acromion. Contracting the long head of the triceps rotates the acromion towards the midline, away from the greater tuberosity. Combining contraction of both of these muscles creates space between the acromion and the greater tuberosity, assisting to prevent impingement of the bursa.
Contract these muscles to externally rotate the humerus and outwardly rotate the scapula when performing postures involving overhead movements. # *
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