Massage & Bodywork

January/February 2012

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Page 49 of 132

EDUCATION FUNCTIONAL ANATOMY Latissimus Dorsi By Christy Cael The latissimus dorsi is a large, superfi cial back muscle that acts strongly on the shoulder. Its broad origin at the thoracolumbar aponeurosis and specifi c insertion on the proximal humerus provide signifi cant leverage on the glenohumeral joint. The fl at fi bers of the latissimus dorsi cover the lower portion of the posterior trunk, then converge and join the teres major to form the posterior border of the axilla. In a small percentage of people, the latissimus dorsi has an attachment on the lateral, inferior portion of the scapula, near the teres major and minor. The latissimus dorsi has a distinct twist in the muscle near its attachment on the humerus. This feature maintains leverage throughout a large range of motion, allowing muscles to produce powerful movements over broad distances. The latissimus dorsi works with the lower fi bers of the pectoralis major, teres major, and the posterior deltoid to pull the arm downward from an overhead position during hitting, swimming, and throwing motions (any position that "unwinds" or fl attens the twist). It also works with the pectoralis major to adduct the arm, pulling objects toward the body, or raising the body when the arm is fi xed, such as during rock climbing. These muscles also work together to prevent downward displacement of the trunk when bearing weight on the arms, like when pushing up from a chair, walking with crutches, or supporting the body on the rings or parallel bars in gymnastics. Adequate mobility in the latissimus dorsi and its synergists is critical for proper performance of overhead movements. When this muscle is shortened or tight, the back arches to compensate, creating compression in the posterior spine. This is a common source of low-back pain in athletes and others performing repetitive overhead movements such as lifting, pulling, pushing, or reaching. Shortness in these muscles may be observed when performing passive shoulder fl exion and abduction with the client supine. These motions will be limited, or the client may compensate by arching her back. Adhesions and trigger points are also common where the latissimus dorsi, teres major, teres minor, and the long head of the triceps brachii merge at the posterior axilla. This may refer pain distally into the upper extremity and limit shoulder mobility. Latissimus dorsi muscle LATISSIMUS DORSI Attachments • Origin: Spinous processes of T7–L5, posterior iliac crest, and posterior sacrum (via thoracolumbar aponeurosis) • Insertion: Medial lip of bicipital groove of the humerus Actions • Adducts, extends, and internally rotates the shoulder Innervation • Thoracodorsal nerve • C6–C8 Celebrate ABMP's 25th anniversary and you may win a refund on your membership. 47

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