How to Identify the Latissimus Dorsi Muscle:
The latissimus dorsi muscle is a huge, triangularly shaped back muscle that helps you do things like pull ups, swimming and even breathing. The lats are superfiscially located, which means they are clearly visible (when the skin is removed). In other words, you don't have to dissect away layers of muscles to locate the lats. And lucky for we non-medical personnel, (in people with well-developed back muscles in particular) you don't absolutely have to remove the skin to notice the lats; you can identify this important back muscle by its shape.
The latissimus dorsi muscle is often called the "lats" for short.
Origin and Insertion of the Lats - Exactly Where the Lats Are Located:
The two ends of a muscle attach the body, usually, but not always, to bone. These places of attachment are known as the origin and insertion of a muscle. When it comes to the lats, the origin is complicated, but the insertion is simple.
The lats muscle originates on top from the bottom six thoracic vertebrae and the last three or four ribs. Part of the origin also includes the thoracolumbar fascia at the level of the lumbar and sacral vertebrae, as well as the back one third of the outside part of the top of your hip bone. And finally, the origin of the lats includes just a tiny little bit of the bottom angle of your shoulder blade.
As the muscle fibers of the lats extend from the origin to the insertion point (the insertion for the lats is located on the inner aspect of your upper arm bone, just below the shoulder joint) they taper into a point. In this way (from a wide origin to a pin pointed insertion), the muscle forms a triangular-like shape.
What the Latissiumus Dorsi Muscle Does for You:
Strong "lats" help you use your arms to pull your body weight up. Good examples of activities that use the lats extensively include doing chin ups, rock climbing and swimming.
The lats also assist with the breathing process. They are called an "accessory breathing muscle," which means they enhance the movements of the trunk during inhale and exhale. They do this by lifting (expanding) the circumference of the rib cage when you inhale, which may increase the volume of air that enters your lungs. During exhale, the latissimus dorsi muscle helps decrease the circumference of the trunk, which may have the effect of squeezing more air out.
With your trunk stationary, the lats turn your arm in, they bring it closer to the mid line of your body and they extend your shoulder joint back (essentially the same as bringing your arm back). They can do these movements separately or in combination with one another.
Other things the latisimus dorsi does is to bring the whole shoulder girdle down (called depression), as well as assist in the act of side bending (called lateral flexion). When both lats are working at the same time they assist with arching the spine (called hyperextension) and with tilting the pelvis anteriorly.
What Happens When Your Lats Muscles Are Weak or Tight:
A weak lats muscle may interfere with bringing your arm toward your body or your body toward your arm. Weakness may also interrupt your ability to laterally flex your trunk.
If your lats are tight or short, it will be hard to take your arm up in front of you, or out to the side. A short latissimus dorsi muscle tends to keep your shoulder girdle down and forward.
If you have a scoliosis (C curve), one side of your lats muscle will likely be tighter than the other. If you have a kyphosis, the front part of your lats will likely be tight.
Kendall, Florence Peterson, McCreary, Elizabeth Kendall, and Provance, Patricia Geise. Muscles Testing and Function with Posture and Pain. 3rd. Baltimore, Maryland: Williams & Wilkins, 1983.
Latissimus Dorsi. GP Notebook website. www.gpnotebook.co.uk/ Accessed April 2 2012.