Latissimus Dorsi Muscle

Original Editor - Ahmed Nassef

Top Contributors - Lucinda hampton, Wanda van Niekerk, Ahmed Nassef, Kim Jackson, Uchechukwu Chukwuemeka, Joao Costa, Wendy Snyders, Admin and George Prudden  

Description

The latissimus dorsi muscle is a broad, flat muscle that occupies the majority of the lower posterior thorax. The muscle's primary function is of the upper extremity but is also considered to be a respiratory accessory muscle. It is relatively thin and covers almost all back muscles at the posterior trunk, except the trapezius.

• Along with the levator scapulae, trapezius and rhomboid muscles, the latissimus dorsi belongs to the superficial layer of the extrinsic back muscles.
• Functionally, the latissimus dorsi muscle belongs to the muscles of the scapular motion. This muscle is able to pull the inferior angle of the scapula in various directions, producing movements on the shoulder joint (internal rotation, adduction and extension of the arm).

Due to this muscle's broad attachment on the spinous processes, ongoing research is looking at what, if any, role the muscle plays in trunk movement. Currently, the evidence is mixed on how much influence this muscle has on spine extension, lateral flexion, or rotation.

Origin and Insertion

The muscle has attachments to the lower six vertebral spinous processes anterior to the attachment of the trapezius on the spinous processes. Through the thoracolumbar fascia latissimus dorsi attaches to the lumbar and sacral spinous processes (T6 to S5 levels), and the supraspinous ligament. Other attachments of the muscle include the posterior iliac crest, lower three to four ribs where it interdigitates with the external oblique muscle and inferior angle of the scapula.

The muscle fibers are situated in various orientations with the uppermost fibers almost horizontally oriented and the lower fibers much more vertically oriented on the thorax.

As the muscle fibers extend toward the axilla, the fibers wind around the anterior aspect of the teres major muscle to insert as a flat tendon on the floor of the intertubercular sulcus.

The latissimus dorsi attachment on the intertubercular sulcus extends farther superiorly than does the attachment of the teres major on the lateral lip of the sulcus.   

Insertion

Floor of intertubercular (bicipital) groove of humerus.

Nerve supply

Thoracodorsal nerve (C6 – C8) from the posterior cord of the brachial plexus, which enters the muscle on its deep surface. 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.

Blood supply

Thoracordosal Artery from the axillary artery

Action

Depression, adducts, extends and internally rotates the arm at the shoulder

Primary Actions of the Latissimus Dorsi

1. Adduction of the arm at shoulder

• Agonists: Pectoralis Major, Teres Major, Triceps Brachii (long head)
• Antagonists: Deltoid (middle) Supraspinatus

2. Extension of the arm at the shoulder

• Angonists: Deltoid (posterior) Triceps brachii (long head), Pectoralis Major (sternal head)
• Antagonists: Deltoid (anterior) Biceps brachii, Coracobrachialis, Pectoralis Major (clavicular head)

3. Internal rotation of the arm at the shoulder

• Agonists: Subscapularis, Deltoid (anterior), Pectoralis Major, Teres Major
• Antagonists: Infraspinatus, Teres minor, Deltoid (posterior)

Secondary Actions of the Latissimus Dorsi

1. Assists with extension of the trunk

• Agonists: Longissimus thoracis, Iliocostalis lumborum, Iliocostalis thoracis
• Antagonists: Rectus abdominis

2. Assists with flexion of the trunk

• Agonist: Rectus abdominis
• Antagonists: Longissimus thoracis, Iliocostalis lumborum, Iliocostalis thoracis

3. Assists with lateral flexion of the trunk

• Agonist: Quadratus lumborum, Rectus abdominis
• Antagonists: Longissimus thoracis, Iliocostalis lumborum, Iliocostalis thoracis

4. Assists with anterior and lateral pelvic tilt

• Agonist: Rectus abdominis
• Antagonists: Semitendinosus, Semimembranosus, Biceps femoris

5. Assists with depression of the scapula

• Agonists: Serratus Anterior (lower fibers), Trapezius (lower fibers), Pectoralis minor
• Antagonists: Levator Scapulae, Trapezius (upper fibers)

6. Assist with protraction of the scapula

7. Assists with deep inspiration and forced expiration

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. Clinicians can palpate for a muscle contraction by holding the posterior axillary fold between the finger and thumb and asking the patient to cough.

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.

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.

Rehabilitation

Latissimus dorsi runs over more than one joint and is therefore classified as a global mobiliser. Global mobilisers may lose extensibility in habitual use or consistent positioning of a joint i.e. poor posture. 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). 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. As a result, limited glenohumeral joint flexion and lateral rotation may be observed.

Assessment

Muscle Flexibility

Muscle Strength

Manual Therapy

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