An upper-body, strength-building regimen would not be complete without the classic pullup, a challenging compound exercise that involves more than one joint and recruits more than one muscle group. The pullup is a body-weight exercise designed to primarily work the muscles in your back, shoulders and arms at the same time. With slight changes in technique, you can shift some of the load and engage other muscles.
The main muscle worked during a pullup is the latissimus dorsi, commonly referred to as the lats. These are your wings -- triangular and fan-shaped -- and are the largest and broadest muscles of your back. The lats run from the middle of your back, along the side of your trunk and attach to your upper-arm bone, underneath your armpit. This muscle is mainly responsible for the adduction, extension and internal rotation of your shoulder. The lats also help pull your shoulder blades down during a pullup.
Without the help of other muscles, called synergists, you would not be able to perform a pullup. The brachialis, brachioradialis and biceps arm muscles are involved when you flex your elbows. The infraspinatus, a rotator cuff muscle, helps with the external rotation of the shoulder, while the teres major and teres minor help with the adduction, extension and internal rotation of your shoulder. At the back of your shoulder is the posterior deltoid, which helps during shoulder extension. Other assisting muscles include the levator scapulae, a neck muscle, three upper back muscles -- the lower and middle trapezius and the rhomboids -- and the pectoralis minor, a chest muscle.
Your triceps, located at the rear of your upper arm, engage during pullups to help stabilize your arm. The triceps consists of three heads -- long, lateral and medial. While all three heads are involved in the extension of your elbow, the long head is more active during shoulder extension and adduction, which occurs when you move your upper arm down as you pull yourself up toward the bar.
Variations for Load Shift
More emphasis is placed on the outer portions of the lats if you use a wider grip, according to Marc Perry, certified strength and conditioning specialist. To shift some of the load to your upper-back muscles, slide your hands closer together. Mike Behnken, NASM certified personal trainer, recommends using a reverse grip to place more emphasis on your biceps. Towel pullups require significant grip strength and because of this, your forearm muscles get hit hard with this pullup variation. A more challenging version, the side-to-side pullup, engages your internal and external obliques.
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