Latissimus dorsi is a broad, flat muscle that connects the mid-back, low-back, and pelvis to the humerus through the thoracic vertebrae, clavicle, and scapula.
Latissimus dorsi has extensive attachments and provides complex functions that are best understood by testing its activity in various motions. Its structure around teres major is similar to pectoralis major where flat fibers are wrapped in twisted fibers that straighten as the arm is raised overhead.
It has statistically significant variations in its attachments. It may cross over the bicipital groove and blend with the attachment of pectoralis major. It may also blend with the fibers of triceps brachii. The lateral fibers may extend all the way down to the ilium. A little more than 40% of the time, it attaches to the inferior angle of the scapula. A little less than 40% of the time, it attaches via soft connective tissue and about 20% of the time there is no attachment to the scapula at all.
Origin – through the lumbar aponeurosis, it attaches to T7-T12, sacrum, and ilium. It also attaches to the last 3-4 ribs along the lateral border of this muscle.
Latissimus dorsi usually attaches to the inferior angle of the scapula, either directly or through fascial slips.
Insertion – the lateral lip of the bicipital groove, usually fused with the tendon of teres major.
Function – it is consistently credited with extension, adduction and assisting internal rotation of the scapula. It is also involved in depression of the scapula and extension of the thoracic spine. It influences neck and pelvic posture.
Tony Preston has a practice in Atlanta, Georgia where he sees clients.
He has written and taught about anatomy, trigger points and cranial therapies since the mid-90s.