Excessive superior or insufficient inferior glide of the humeral head is noted during shoulder motions.  This may be associated with stiffness or shortness of the superior or inferior structures of the GH joint.  Insufficiency of the rotator cuff because of weakness, recruitment impairments, or tear is a major causative factor. This disrupts the normal force couple between the rotator cuff and the deltoid. (Sahrmann, 2002)