The upper body has a significant range of movement, and therefore it has a significant number of muscles to coordinate all the movement. Like the muscles of the legs, they can be grouped to simplify the discussion. The major muscle groups of the upper body are the back, chest, shoulders and arms.
Back
The muscles of the back include the latissimus dorsi (lats), trapezius (traps), and rhomboids. These muscles allow for shoulder adduction, extension, internal rotation of the arm, transverse extension and scapular depression, adduction, downward rotation, upper rotation, elevation, and extension of the neck and lower back.
Chest
The chest is made up of the pectoral (pecs) muscles (major and minor). These muscles run from your arms toward the center of your chest. At the shoulder, the pecs perform transverse flexion and adduction, internal rotation adduction and extension. Movements that activate the pecs tend to be in a pushing motion, or a squeezing motion (like a hug).
Shoulders
The shoulders are composed of the deltoids and the rotator cuffs. The deltoids have three heads, the anterior, lateral and posterior. The deltoids extend the arms in all directions, as well as rotate them at the shoulders. The rotator cuff is made up of four muscles: the supraspinatus, infraspinatus, teres minor, and subscapularis. The rotator cuff is responsible for stabilizing the shoulder joint and for creating rotation of the arm in all movements.
Arms
The muscles of the arms are the biceps brachii (biceps for short) and triceps brachii (triceps for short). Each has their name based on the number of heads in the muscle. Two heads for the biceps and three heads for the triceps. The biceps muscle has three functions: elbow flexion, wrist supination (rotating palm toward the sky) and shoulder flexion. The triceps has two functions: elbow extension and shoulder extension.
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