Latissimus dorsi muscle

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Latissimus Dorsi
Latissimus dorsi.png
Latissimus dorsi
File:Latissimus dorsi.PNG
Muscles connecting the upper extremity to the vertebral column.
Details
Latin Musculus latissimus dorsi
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
Thoracodorsal branch of the subscapular artery
Thoracodorsal nerve
Actions Adducts, extends and internally rotates the arm when the insertion is moved towards the origin. When observing the muscle action of the origin towards the insertion, the lats are a very powerful rotator of the trunk.
Antagonist Deltoid and trapezius muscle
Identifiers
Dorlands
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FMA {{#property:P1402}}
Anatomical terms of muscle
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The latissimus dorsi (/ˌləˈtɪsᵻməs ˈdɒrsaɪ/) (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.

Structure

Variations

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Axillary arches shown from two different angles.

The number of dorsal vertebrae to which it is attached varies 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% of the population 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.[1]

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.[2][3] This muscular form is found in ~5% of humans and is sometimes termed the latissimocondyloideus.[2]

The latissimus dorsi crosses the inferior angle of the scapula. A study found that, of 100 cadavers dissected:[4]

  • 43% had "a substantial amount" of muscular fibers in the latissimus dorsi originating from the scapula.
  • 36% had few or no muscular fibers, but a "soft fibrous link" between the scapula and the latissimus dorsi
  • 21% had little or no connecting tissue between the two structures.

Triangles

  • 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.

Innervation

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.[5]

Function

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.[citation needed] It also has a synergistic role in extension (posterior fibers) and lateral flexion (anterior fibers) of the lumbar spine, and assists as a muscle of both forced expiration (anterior fibers) and an accessory muscles of ispiration (posterior fibers).[6]

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.

Training

The power/size/strength of this muscle can be trained with a variety of different exercises. Some of these include:

Lifting under control can help reduce chances of injury.

Clinical relevance

Tight latissimus dorsi has been shown to be one cause of chronic shoulder pain and chronic back pain.[7] 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.[8]

The latissimuus dorsi is a potential source of muscle for breast reconstruction surgery after mastectomy or to correct pectoral hypoplastic defects such as Poland's syndrome.[9][10] An absent or hypoplastic latissimus dorsi can be one of the associated symptoms of Poland's syndrome.[11][12]

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

  • Latissimus dorsi muscle animation.gif

    Position of the latissimus dorsi muscle (shown in red). Animation.

  • Latissimus dorsi muscle animation3.gif

    Animation. Rib cage is not shown, except for 10th rib, 11th rib and 12th rib.

  • Lumbar triangle

  • Slide9m.JPG

    Latissimus dorsi muscle

  • Slide9111.JPG

    Latissimus dorsi

  • Slide2Nemio.JPG

    Anterior thoracic and abdominal wall.Superficial dissection.Anterior view.

  • Full back muscle flex showing the latissimus dorsi muscle

See also

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This article uses anatomical terminology; for an overview, see Anatomical terminology.

References

This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

  1. ↑ 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.
  2. ↑ Haninec P, Tomás R, Kaiser R, Cihák R., Development and clinical significance of the musculus dorsoepitrochlearis in men, Clin Anat. 2009 May;22(4):481-8. PMID 19373904.
  3. ↑ Edwards, William E., The Musculoskeletal Anatomy of the Thorax and Brachium of an Adult Female Chimpanzee,6571st Aeromedical Research Laboratory, New Mexico, 1965. [1]
  4. ↑ https://books.google.com/books?id=EGM73_guZB8C&pg=PA16&dq=latissimus+dorsi+scapula&hl=en&sa=X&ei=CDRSVeSOHpL0oAT32IGIBQ&ved=0CDUQ6AEwAg#v=onepage&q=latissimus%20dorsi%20scapula&f=false
  5. ↑ 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
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Arnheim, D.D., Prentice, W.E., Principles of athletic training. 9th ed. McGraw Hill, pp 570-574, 1997.
  8. ↑ Francis, P., Applied anatomy and kinesiology, supplemental materials. KB Books., p 19-25, 1999.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.

External links

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