Bear with me as we talk about the core back muscles. Trust me that it will all come together within the next few weeks. Let’s start with the latissimus dorsi (lats for short). We often think of your lats as being used during swimming, but they do more. Your lats are the largest (not thickest) muscles in your body, they cover a greater area than any other muscle.
Where are they located? They are large, triangular and flat muscles attached to the body in several places: They attach at the T7 – L5 sections of your spine, the iliac crest of the sacrum (think of the bottom of your spine above what you might call your tailbone), they attach to your scapula and also to your lower 3 or 4 ribs. The lats attach to your humorous bone as well. Whew, that’s quite an expanse!
What is their job? They are responsible for extension, adduction, the transverse extension is also known as horizontal abduction, flexion from an extended position, and (medial) internal rotation of the shoulder joint. In layman’s terms, they medially rotate your arm at the shoulder (turns your arm in), adducts your arm (brings the arm towards the middle of your body), extends the arm at the shoulder (when your reaching for someone’s hand in a handshake).
To feel them, reach under your arm, below the armpit where your ribs are, the piece of muscle that you see/feel is part of your latissimus dorsi. Swimmers normally have well-developed lats, as do bodybuilders.