Reflection 3 - Scapulohumeral Rhythm

The scapulohumeral rhythm is the ratio of movement between the scapula and the humerus. It is a kinematic interaction between the scapula and the humerus. This states that for full 180 degrees of motion, the scapulothoracic joint produces 60 degrees of movement, while the humerus produces 120 degrees of motion. Scapulohumeral rhythm is important because it allows muscles to be in an optimal length-tension relationship. It helps maintain subacromial space. Another reason that scapulohumeral rhythm is important is because it helps prevent active insufficiency of the glenohumeral joint. In terms of range of motion, the humeral head must always rotate laterally. For the body to have scapulohumeral rhythm, motion must be distributed between 2 joints. With scapulohumeral rhythm, joint congruency results in decreased shear forces.