Latissimus dorsi muscle
|Muscles connecting the upper extremity to the vertebral column.|
|Latin||Musculus latissimus dorsi|
|Gray's||subject #121 432|
|Origin||Spinous processes of vertebrae T7-L5, thoracolumbar fascia, iliac crest, inferior 3 or 4 ribs and inferior angle of scapula|
|Insertion||Floor of intertubercular groove of the humerus|
|Artery||Thoracodorsal branch of the subscapular artery|
|Actions||Adducts, extends and internally rotates the arm|
|Antagonist||Deltoid and trapezius muscle|
The latissimus dorsi (plural: latissimi dorsi), meaning 'broadest [muscle] of the back' (Latin latus meaning 'broad', latissimus meaning 'broadest' and dorsum meaning the back), is the larger, flat, dorso-lateral muscle on the trunk, posterior to the arm, and partly covered by the trapezius on its median dorsal region. Latissimi dorsi are commonly known as "lats", especially among bodybuilders.
The latissimus dorsi is responsible for extension, adduction, transverse extension also known as horizontal abduction, flexion from an extended position, and (medial) internal rotation of the shoulder joint. It also has a synergistic role in extension and lateral flexion of the lumbar spine.
Due to bypassing the scapulothoracic joints and attaching directly to the spine, the actions the latissimi dorsi have on moving the arms can also influence the movement of the scapulae, such as their downward rotation during a pull up.
The number of dorsal vertebra to which it is attached vary from four to eight; the number of costal attachments varies; muscle fibers may or may not reach the crest of the ilium.
A muscular slip, the axillary arch, varying from 7 to 10 cm in length, and from 5 to 15 mm in breadth, occasionally springs from the upper edge of the latissimus dorsi about the middle of the posterior fold of the axilla, and crosses the axilla in front of the axillary vessels and nerves, to join the under surface of the tendon of the pectoralis major, the coracobrachialis, or the fascia over the biceps brachii. This axillary arch crosses the axillary artery, just above the spot usually selected for the application of a ligature, and may mislead a surgeon. It is present in about 7% os and may be easily recognized by the transverse direction of its fibers. Guy et al. extensively described this muscular variant using MRI data and positively correlated its presence with symptoms of neurological impingement.
A fibrous slip usually passes from the upper border of the tendon of the Latissimus dorsi, near its insertion, to the long head of the triceps brachii. This is occasionally muscular, and is the representative of the dorsoepitrochlearis brachii of apes.
- The lateral margin of the latissimus dorsi is separated below from the obliquus externus abdominis by a small triangular interval, the lumbar triangle of Petit, the base of which is formed by the iliac crest, and its floor by the obliquus internus abdominis.
- Another triangle is situated behind the scapula. It is bounded above by the trapezius, below by the latissimus dorsi, and laterally by the vertebral border of the scapula; the floor is partly formed by the rhomboideus major. If the scapula is drawn forward by folding the arms across the chest, and the trunk bent forward, parts of the sixth and seventh ribs and the interspace between them become subcutaneous and available for auscultation. The space is therefore known as the triangle of auscultation.
- The Latissimus Dorsi can be remembered best for insertion as "The Lady Between Two Majors". As the Latissimus Dorsi inserts into the floor of the intertubercular groove of the humerus it is surrounded by two major muscles. The Teres Major inserts medially on the medial lip of the intertubercular groove and laterally the Pectoralis Major inserts into the lateral lip.
The Latissimus dorsi is supplied by the sixth, seventh, and eighth cervical nerves through the thoracodorsal (long scapular) nerve. Electromyography suggests that it consists of six groups of muscle fibres that can be independently coordinated by the central nervous system.
The power/size/strength of this muscle can be trained with a variety of different exercises. Some of these include:
- Vertical pulling movements such as pull-downs and pull-ups (including chin-ups)
- Horizontal pulling movements such as bent-over row, T-bar row and other rowing exercises
Lifting under control can help reduce chances of injury.
Other types of sport and exercise are known to generate lat growth and power, such as boxing. In boxing the large number of punches thrown by a fighter on a day to day basis in training, sparring, padwork contributes to development of the lat muscles. Examples of this would be seen in boxers such as Manny Pacquiao, Chris Eubank, Sam Storey, Carl Froch and Arturo Gatti, although the size difference in lats can be due to genetics as well.
Most latissimus dorsi exercises concurrently recruit the teres major, posterior fibres of the deltoid, long head of the triceps brachii, among numerous other stabilizing muscles. Compound exercises for the 'lats' typically involve elbow flexion and tend to recruit the biceps brachii, brachialis, and brachioradialis for this function. Depending on the line of pull, the trapezius muscles can be recruited as well; horizontal pulling motions such as rows recruit both latissimus dorsi and trapezius heavily.
Tight latissimus dorsi has been shown to be one cause of chronic shoulder pain and chronic back pain. Because the latissimus dorsi connects the spine to the humerus, tightness in this muscle can manifest as either sub-optimal glenohumeral joint (shoulder) function which leads to chronic pain or tendinitis in the tendinous fasciae connecting the latissimus dorsi to the thoracic and lumbar spine.
Cardiac support 
For heart patients with low cardiac output and who are not candidates for cardiac transplantation, a procedure called cardiomyoplasty may support the failing heart. This procedure involves wrapping the latissimus dorsi muscles around the heart and electrostimulating them in synchrony with ventricular systole.
Additional images 
- Guy MS, Sandhu SK, Gowdy JM, Cartier CC, Adams JH. MRI of the axillary arch muscle: prevalence, anatomic relations, and potential consequences. AJR Am J Roentgenol. 2011 Jan;196(1):W52-7.
- Brown JM, Wickham JB, McAndrew DJ, Huang XF. (2007). Muscles within muscles: Coordination of 19 muscle segments within three shoulder muscles during isometric motor tasks. J Electromyogr Kinesiol. 17(1):57-73. PMID 16458022 doi:10.1016/j.jelekin.2005.10.007
- Arnheim, D.D., Prentice, W.E., Principles of athletic training. 9th ed. McGraw Hill, pp 570-574, 1997.
- Francis, P., Applied anatomy and kinesiology, supplemental materials. KB Books., p 19-25, 1999.
|Wikimedia Commons has media related to: Latissimus dorsi muscles|
- LUC lat
- latissimus dorsi at GPnotebook
- SUNY Figs 01:03-08 - "Superficial layer of the extrinsic muscles of the back."
- Cross section at UV pembody/body8a