Performing push-ups works a variety of muscles in your upper body, including specific muscles within your abdomen, chest, shoulders and upper arms. You can vary your technique by placing your hands at different widths to emphasize one area over another. To improve the endurance and strength of the muscles you're working, gradually increase the number of push-ups you perform each day .
The rectus abdominis and transversus abdominis contract continually while you perform push-ups, to hold your body off the floor and keep your legs and torso aligned. The rectus abdominis spans the front of your abdomen and is the most prominent of the abdominal muscles. The transversus abdominis lies deep within the abdomen, wrapping around the entire abdominal area. Both muscles compress the abdomen, and the rectus abdominis also flexes the spine forward, although it does not execute this function when you perform push-ups.
The anterior portion of the deltoid muscle is one of the major shoulder-joint horizontal adductors, moving your upper arms toward your chest during the upward phase of a push-up. It also helps control the speed of movement during the downward phase. The deltoid attaches to parts of the clavicle and scapula, just above the shoulder joint, on one end, and to the outside of the humerus bone on the other. Along with horizontal adduction, the anterior deltoid assists with flexion and internal rotation of the humerus within the shoulder socket.
The pectoralis major is another main horizontal adductor of the shoulder joint, so it performs the same functions as the anterior deltoid during a push-up. It also contributes to adduction, extension, flexion and internal rotation ranges of motion. The muscle is divided into clavicular and sternal parts. Both parts attach just outside the head of the humerus and run toward the center of your body. The parts then separate, with the clavicular part attaching to the inner two-thirds of the clavicle, and the sternal part to the front of the sternum and the first six ribs.
While the anterior deltoids and pectoralis major muscles work to horizontally adduct the upper arms during the upward phase of a push-up, the triceps brachii muscles, or triceps for short, are also hard at work extending the elbow joints so you can fully extend your arms. The triceps also control the speed of elbow-joint flexion during the downward phase of the exercise. The closer together you place your hands during a push-up, the harder the triceps work. The muscle is divided into three heads -- the lateral head, long head and medial head. The lateral and medial heads attach to the back of the humerus bone and the long head attaches just behind the shoulder socket on one end; all three heads combine and attach to the back of your elbow on the other.
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