Serratus Anterior Contraction
When the serratus magnus contracts it protracts and upwardly rotates the shoulder girdle at acromioclavicular and sternoclavicular joints and stabilizes the scapula against the thoracic wall. Due to its involvement in a punching motion, the serratus anterior is the “boxer’s muscle”. In a clinical setting, the forgotten serratus anterior can be tested by having the patient’s glenohumeral joint around 120° of flexion, humeroulnar joint in extension, and while resisting downward pressure on the upper limb, during which the serratus anterior can be seen and palpated. During testing, the medial border of the scapula can also be palpated for any “winging”, as if the serratus magnus is weak or paralyzed, the medial border of the scapula will be more prominent, giving it the “winged scapula” appearance.