The Latissimus Dorsi (AKA the Lat), is a large, multiaction muscle. When the Lats are strong and consistently trained, they create the V shape seen on someone’s back. The Lats attach to thoracic vertebrae T6-T12, ribs 8-12, and the Iliac crest and they wrap up under the arm and insert on the medial lip of the Intertubercular Groove of the humerus. The Latissimus Dorsi is innervated by the Thoracodorsal Nerve, a branch off the brachial plexus of C6-C8.
The lats are responsible for both arm movement and trunk stability.
In terms of arm movement, they adduct the arm or bring the arm to your side, extend the arm or bring the arm backwards, and internally rotate the arm. This translates functionally to lifting and pulling. Strong Lats help support the smaller muscle of the rotator cuff, the Subscapularis.
The lats, making up a large portion of our backs, also help extend the trunk. This is important for helping with upright posture. Additionally, they assist with side bending our trunks.
Although the lats play an important part in assisting good posture, they can also work against us if they are too tight. Because the proximal or upper portion of the lat wraps under our arm and inserts on the medial side of the humerus, a tight lat can round our shoulders forward. This can alter the mechanics of the shoulder and cause pain due to impingement. Tightness in the lats can also limit overhead shoulder range of motion. This can result in pain with reaching overhead or with lifting or lowering something above shoulder height. Thirdly, lat tightness can cause pain along the ribs and back, due to the tightness restricting spinal and rib mobility.
Weakness in the lats can also cause a number of issues. If you do not have strong lats, then you are missing an important muscle to help with day to day lifting. This will result in increased work demand on the other muscles, placing your shoulder and back at risk for pain and injury.
