Shoulder Anatomy: Latissimus Dorsi

MUSCLE OF THE DAY: “Latissismus Dorsi”

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The latissimus dorsi muscle, “latissimus” in latin = broadest, “dorsum” = back, is the widest muscle in the human body. It is thin and covers all other back muscles except for the trapezius. It spans over the lumbar and lower thoracic regions of the back and is generally considered to have four parts, vertebral, costal, iliac and scapular. The lats are classified as a superficial, posterior extrinsic (axioappendicular) muscle along with the levator scapulae, trapezius and rhomboids. It is also part of an important anatomical landmark, the auscultation triangle, at which a doctor uses a stethoscope to listen to the heart and lungs (blow your doc away at your next check-up and tell them the Show Up crew taught you that). The borders of the triangle are the trapezius superiorly, medial border of scapular and the latissimus dorsi inferiorly.

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Origin(s) (proximal attachment): Vertebral part: spinous processes of the 7th to 12th thoracic vertebrae and the thoracolumbar fascia. Costal part: 9 th to 12 th ribs. Iliac part: Iliac crest of the pelvic girdle. Scapular part: Inferior angle of the scapula.

Insertion (distal attachment): Intertubercular sulcus (bicipital groove) of the humerus, between pectoralis major and teres major muscles. Insertion mnemonic: Lady between two majors.

Action(s): DIE HARD = Depress, Internally rotate, Extend, Horizontally abduct, Adduct, Retract, Downwardly Rotate. Also assists in respiration during forced expiration.

Common Injuries to Latissimus Dorsi:

Latissumus dorsi strains are often caused by overuse, poor posture, poor technique in sports or recreational activities and exercising without warming up. Due to the size and coverage of the lats, an injury can cause pain in the lower, middle and upper back, back of the shoulders, base of the scapula and the inside of the arms down to the fingers. Serious damage or strains can cause other symptoms such as tingling in the lower arms, difficulty breathing and tendinitis in the middle and lower back. It is possible to fully tear or rupture the latissimus dorsi but is rare and only seen in athletes, particularly golfers, baseball pitchers and gymnasts. In most cases, lat pain will go away with rest, stretching and strengthening. For more specifics, check out our partner's in crime, the Prehab Guys!

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Related Study/Journal Article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3981267/