The pushup is a basic movement that primarily works the pectoralis major of the chest, which is a two-headed muscle group comprised of an upper and lower head. The pushup also works several other muscles, all of which act as assisting movers during the movement. These muscles are the anterior deltoid, triceps brachii long head, triceps brachii lateral head, triceps brachii medial head and anconeus. In addition to the primary and assisting movers, the pushup also involves other muscles that act as stabilizers, or joint-fixators.
The posterior deltoid and rotator cuff muscles act as stabilizers of the shoulder joint during the pushup. The rotator cuff also stabilizes the scapula throughout the movement. The posterior deltoid is located at the back of the deltoid muscle group. The subscapularis of the rotator cuff is located at the front of the scapula, or shoulder blade. The supraspinatus, infraspinatus and teres minor of the rotator cuff are located at the back of the scapula. The serratus anterior, although not a shoulder muscle, also stabilizes the scapula during the pushup. This muscle is located at the upper eight or nine ribs.
There are two muscle groups of the back that function as stabilizers while you do pushups. Those muscle groups are the rhomboids and the erector spinae. The rhomboid major and rhomboid minor are located at the middle to upper back region, underneath the middle trapezius muscle of the back. The erector spinae, comprised of the iliocostalis, longissimus and spinalis, extends from the back of neck down to the lower back region.
The rectus abdominis acts as a stabilizer of the spine, opposite to the erector spinae, during the pushup. This muscle extends from the sternum down to the pubis of the hip. The rectus abdominis is the muscle that gives the six pack appearance of the stomach.
Hips and Legs
The largest and strongest muscle of the body, which is the gluteus maximus, stabilizes the hip while you perform the pushup. This muscle comprises an upper head and a lower head. It is located in the buttocks region, lying over the gluteus medius and gluteus minimus. The quadriceps of the front thigh is another muscle group that acts as a stabilizer of the pushup. It is made up of four muscles, hence the name of the muscle group. Those muscles are the rectus femoris, vastus medialis, vastus lateralis and vastus intermedius. All of these muscles work to stabilize the knee joint.