Kinematic changes have been thought to be present in people with symptoms of impingement and to result in further decreases in the available supraspinatus muscle outlet or suprahumeral space.15,17–19 Motions that bring the greater tuberosity in closer contact with the coracoacromial arch20 are particularly problematic. These motions include excessive superior or anterior translations of the humeral head on the glenoid fossa, inadequate lateral (external) rotation of the humerus, and decreases in the normal scapular upward rotation and posterior tipping on the thorax, all occurring during humeral elevation. These kinematic changes have all been purported to occur in patients with symptoms of impingement.15,17–20 Additionally, the hypothesized kinematic alterations in scapular motion have been linked to decreases in serratus anterior muscle activity, increases in upper trapezius muscle activity, or an imbalance of forces between the upper and lower parts of the trapezius muscle.17,19,21