Latissimus Dorsi Muscle

Description

The latissimus dorsi muscle, whose name means “broadest muscle of the back,” is one of the widest muscles in the human body. Also known as the “lat,” it is a large, flat triangular muscle that is not used strenuously in common daily activities but is an important muscle in many exercises such as pull-ups, chin-ups, lat pulldowns, and swimming.[1] The muscle runs between the trunk, via an extensive attachment and the humerus by a narrow tendon.[2] It therefor, acts on the shoulder joint. The superior border of latissimus dorsi forms the lower border of the triangle of auscultation.[2] The lateral border of the muscle forms the medial border of the lumbar triangle.[2]

Origin

Latissimus-dorsi.jpg

a. Spinous processes of 7th thoracic to 5th Lumbar vertebrae.

b. Iliac crest of sacrum.

c. Thoracolumbar fascia.

d. Inferior angle of the scapula.

e. Lower three or four ribs.[3]

Insertion

Floor of intertubercular (bicipital) groove of humerus.[3]

Nerve supply

Thoracodorsal nerve (C6 – C8)[4] from the posterior cord of the brachial plexus, which enters the muscle on its deep surface.[2] The skin covering the latissimus dorsi muscle is supplied by roots T4 to T12, inclusive by both ventral and dorsal rami, as well as the dorsal rami of L1 to L3.[2]

Blood supply

Thoracordosal Artery from the axillary artery[4]

Action

Depression, adducts, extends and internally rotates the arm at the shoulder[4]

Primary Actions of the Latissimus Dorsi

1. Adduction of the arm at shoulder

2. Extension of the arm at the shoulder

3. Internal rotation of the arm at the shoulder

Secondary Actions of the Latissimus Dorsi

1. Assists with extension of the trunk

2. Assists with flexion of the trunk

3. Assists with lateral flexion of the trunk

4. Assists with anterior and lateral pelvic tilt

5. Assists with depression of the scapula

6. Assist with protraction of the scapula

7. Assists with deep inspiration and forced expiration [5]

Palpation

The lateral aspect of the latissimus dorsi muscle builds the posterior border of the axilla. It is felt to contract during resisted adduction of the arm. Its insertion lies anteriorly at the crest of the lesser tuberosity. By asking a patient to raise his/her arm to 90% flexion and hold it steady against an upwardly directed pressure, the latissimus dorsi muscle can be made to stand out relative to the thorax.[2] Clinicians can palpate for a muscle contraction by holding the posterior axillary fold between the finger and thumb and asking the patient to cough.[2]

Functional Activity

Latissmus dorsi is a climbing muscle. With the arms fixed above the head, it can raise the trunk upwards, together with the help of pectoralis major. It is an important muscle in rowing, swimming (especially during the downstroke) and chopping. The muscle is also active in violent expiration, as it attaches to the ribs. During a cough or sneeze, the muscle can be felt pressing forcibly inward, as it acts to compress the thorax and abdomen.[2]

The muscle assists in holding the scapula against the thorax during upper limb movements. The attachment of the muscle to the inferior angle of the scapula allows this.

In activities such as walking with crutches, where the humerus becomes the fixed point when standing, latissimus dorsi has the ability to pull the trunk forwards relative to the arms. With this action there is also a lifting of the pelvis. In people with paralysis of the lower half of the body, the fact that latissimus dorsi attaches to the pelvis and the fact that it is still innervated, enables the person to produce movement of the pelvis and trunk. As a result of this, people wearing calipers and using crutches can achieve a modified gait by fixing the arms and hitching the hips by alternative contraction of each latissimus dorsi.[2]

Rehabilitation

Latissimus dorsi runs over more than one joint and is therefore classified as a global mobiliser.[6] Global mobilisers may lose extensibility in habitual use or consistent positioning of a joint i.e. poor posture.[7] When contracting, the latissimus dorsi muscle produces torque and force to achieve its function (in this case extension, adduction and medial rotation of the glenohumeral joint).[8] As mentioned previously, latissimus dorsi is a global mobiliser and has the structural characteristics of a global mobiliser, Therefore, the muscle will shorten, as in most cases a painful shoulder would be held in an arm by side position. Furthermore, the muscle will atrophy in the presence of pain or a lengthy period of poor positioning/posture.[6] As a result, limited glenohumeral joint flexion and lateral rotation may be observed.

Assessment

Muscle Flexibility

Muscle Strength

Manual Therapy

[11]

Latissimus Dorsi Stretches

Begin this latissimus dorsi stretch standing tall with your back straight and hands above your head. Gently lean to one side until you feel a mild to moderate stretch in the side of your upper back and shoulder (figure 2). Hold for 5 seconds and then return to the starting position. Repeat 10 times provided the exercise is pain free. Then repeat the exercise on the opposite side.

References

  1. Heydemann A. Severe murine limb-girdle muscular dystrophy type 2C pathology is diminished by FTY720 treatment. Muscle & Nerve. 2007; 56(3):486-494
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Palastanga N, Field D, Soames R. Anatomy and Human Movement: Structure and Function. 5th Ed. Edinburgh. Butterworth Heinemann. Elsevier. 2007.
  3. 3.0 3.1 Drake R L, Vogl AW, Mitchell A W. Gray's Anatomy for Students. 2nd Edition. Philadelphia:Churchill Livingstone, 2010
  4. 4.0 4.1 4.2 Calais-German B. Anatomy of Movement. Seattle: Eastland Press, 1993.
  5. Schünke M, Schulte E, Schumacher U. Prometheus: Lernatlas der Anatomie. Stuttgart/New York: Georg Thieme Verlag, 2007.
  6. 6.0 6.1 Comerford MJ & Mottram SL. Functional stability re-training: principles and strategies for managing mechanical dysfunction. Manual Therapy. 2001;6:3-24.
  7. Dawood M, Bekker PJ, van Rooijen AJ, Korkie E. Inter- and intra-rater reliability of a technique assessing the length of the Latissimus Dorsi muscle. South African Journal of Physiotherapy. 2018;74: a388. (last accessed 01/08/2019)
  8. Herrington L & Horsley I. Effects of Latissimus Dorsi length on shoulder flexion in canoeists, swimmers, rugby players, and controls. Journal of Sport and Health Science. 2014;3: 60-63.
  9. MikeReinold.com.Assessing for Lat and Teres Tightness with Overhead Mobility.Published on Jan 27, 2016. Available from https://www.youtube.com/watch?v=I-sy4d_AuPY[last accessed 01/08/2019]
  10. Brent Brookbush. Latissimus Dorsi Muscle Length Test (Lat Length Test)Published on Aug 9, 2015. Available from https://www.youtube.com/watch?v=-LBBVhc4tO0 [last accessed 01/08/2019]
  11. MikeReinold.com. Latissimus Dorsi Soft Tissue Manual Therapy. Published on May 20, 2018. Available from https://www.youtube.com/watch?v=xCnQj8-MdjM