Push-ups on your toes engage most of the muscles of your body to maintain a straight line from your head to your heels. The United States Army includes the push-up as part of its physical training and testing programs. A low score in the physical fitness test can affect a soldier's military career. The American Council on Exercise includes the push-up as a test for muscular endurance as part of their personal training certification program.
Neck
The muscles of your neck work to hold your head up in a straight line with your trunk. According to Paul Chek of the Corrective High-performance Exercise Kinesiology Institute, your head is about eight percent of your body weight. Your traps, splenius capitis, semispinalis and the upper portion of your erector spinae muscles are engaged to hold up a head as heavy as a 12-pound dumbbell. The traps muscle is the muscle you feel when you rub the back of your neck. The splenius capitis is directly underneath your traps, running at a diagonal from behind your ears toward the spine. Your semispinalis and erector spinae muscles are the deep muscles lying along your spine bones.
Pecs, Triceps and Deltoids
Push-ups obviously work the muscles of your chest, your pectoralis major and pectoralis minor. The pectoralis major arises on your clavicle, breast bone and cartilage of your ribs then inserts on your arm. The pectoralis minor originates on your second to fifth ribs then inserts on a bony protrusion from your shoulder blade. Your pectoral muscles contract and lengthen as you lower your chest towards the floor. They contract and shorten when you push your body back up. The anterior deltoid and triceps muscles function in the same way. Both contract and lengthen on the downward phase, and then contract and shorten on the upward phase. Your anterior deltoid is the front of your shoulder muscle, arising on your collar bone then inserting on your arm. Your triceps lie on the back of your arm, originating on your shoulder blade and arm then inserting at your elbow.
Core
The core is made up of the abdominal and lower back muscles. Your abdominal muscles include the rectus abdominus which runs from the front of your rib cage down to your pelvis; the obliques lie diagonally between your pelvis and the outer edges of your lower back; the transverse muscle goes from one side of the outer edge of your lower back to the other; and your quadratus muscle lies at the back of your abdominal cavity running from the back of your last rib to the back of your hip bones. Your lower back muscles include the lower regions of your spinal erector muscles and your multifidus muscle. These muscles run along the bones of your spine. The lower back muscles work to prevent your spine from flexing forward. Your transverse abdominus compresses your abdominal organs back into your abdominal cavity, drawing your navel toward your spine. The oblique muscles work together to prevent your trunk from rotating sideways.
Lower Body
Your glutes are engaged during a push-up to keep your hips extended. Your quad muscles, the muscles on the front of your thighs, must also activate to keep your knees straight. The muscles of your calves, your gastrocnemius and your soleus, isometrically contract to push your toes against the floor to prevent your ankles from moving. An isometric contraction is a contraction in which your muscle neither shortens or lengthens. The muscles of your lower body function to keep your hips and lower body in-line with your trunk and head.
Shoulder and Hip Joint Stabilizers
There are smaller muscles surrounding the head of your arm and thigh bones. Though these muscles are activated especially during rotational movements, their primary role is to stabilize the head of these bones within the joint cavity. These muscles work to keep your shoulders and hips in place as you do a push-up.
Shoulder and hip stabilizer muscles are easily injured when the larger muscles are over-developed. This often happens when you use exercise machines more than free weight and body weight exercises such as push-ups.
References
- United States Army Physical Fitness Test: Push-ups
- "Personal Trainer Manual"; American Council on Exercise; 1997
- "Equal But Not The Same, Considerations for Training Females"; C.H.E.K. Institute; 1997
