What Muscles Do Pull Ups Work Out?

Pull-ups are usually regarded as an exercise for the back and are lauded for their effectiveness by people who can actually do them. The muscles of the middle back are in fact the primary movers in this well-known body-weight exercise. However, many more muscles play important roles in pull-ups, even if you "cheat" by doing assisted pull-ups with a machine that allows you to lift only a portion of your body weight.

Latissimus Dorsi

The latissimus dorsi muscle is the prime mover for a pull-up. The terms prime mover and agonist refer to the main muscle or muscles worked during a particular exercise. The latissimus dorsi, or lats, is the muscle group of the middle back. The lats extend and adduct the shoulder, according to "A Guide to Personal Fitness Training" by Mary Yoke, M.A. You may have seen this muscle on someone not wearing a shirt that contributes to a nice-looking "V" shape in the back. Shoulder adduction refers to moving your shoulder closer to the midline of your body. During a pull-up, this is accomplished when the upper arm is brought toward the side of the body as you pull your body upward. Shoulder extension in the case of a pull-up is what happens when the shoulders and arms are pulled back as you finish the exercise.

Assistor Muscles

The assistor muscles help the lats in some way during a pull-up. The assistor muscles worked during pull-ups include the muscles of the forearms, upper back, shoulders and chest. Specifically, the muscles worked are the brachialis, brachioradialis, teres major, rear deltoid, rhomboids, levator scapulae, trapezius and the pectoralis major and minor. They provide stability by contracting as your body moves up and down during a pull-up.

Upper Arm Muscles

Both the bicep and triceps muscles of the upper arm are used to do a pull-up, though neither is going to be targeted like a prime mover. Biceps is short for biceps brachii, which refers to both the long and short bundles of the bicep muscles in the front of the upper arm. This is fitting since bi means two. The triceps, or tri for three, on the back of the arm are made up of three bundles, although only the long head bundle of the triceps is used in a pull-up. The stabilizers support the lats by activating when the lats do, even though they are not responsible for the movement of the shoulder joint. Although these muscles are worked during a pull-up, do not expect to see vast improvements in muscle tone as you would for the lats.