#rotatorcuff functions to maintain a centralized congruous glenohumeral joint relationship. Top left x ray is a normal shoulder showing center of the humeral head is lined up with the center of glenoid. Bottom left shows bony architecture of the shoulder -- no bony socket . Bottom right shows how rotator cuff envelopes and wraps around the top of the humeral head to "grab" onto it and keep the humeral head centralized and depressed in line with the glenoid. Top right is x ray of an individual with complete loss of rotator cuff due to chronic tear -- the humeral head has shifted upward abutting against the undersurface of acromion above ( this is impingement on 'steroids😬'! Weak or absent rotator cuff creates an imbalanced muscular pull by the strong deltoid upward. The shoulder joint is in a CONSTANT fight - balance and counter balance, between the deltoid, that tend to displace the centered position of the humeral head upward, and the rotator cuff that pull the humeral head down to maintain centered alignment. Muscle imbalance allows upward migration-- causing "IMPINGEMENT "! Aha... problem is NOT in the acromion above, but the WEAK rotator cuff below! Weight lifting while neglecting a balanced strengthening of the rotator cuff will doom the individual to "impingement ", shoulder pain and rotator cuff tear....then a visit to the operating room... not good😩!