The primary muscle of the chest is the pectoralis major (or pecs). The movements performed by the pectoralis major include pushing with the arms as in bench press and pushups, and bringing the arms together as in a dumbbell flye. The pecs can be further divided into upper, middle and lower pecs. More emphasis is placed on the upper pecs by performing movements on an incline such as dumbbell incline press or incline flyes. The middle pec is emphasized with movements performed on a flat bench while the lower pec is worked using a decline bench.

The back is comprised of a number of different muscles. The major muscles of the back include the latissimus dorsi (lats), rhomboids, middle and lower trapezius and erector spinae muscles. The lats are mainly involved in pulling motions such as rowing and chinning movements. The lats are also worked with dumbbell pullovers. The rhomboids and middle and lower trapezius muscles function to rotate and pull the shoulder blades together. They are primarily used in rowing and chinning movements. The erector spinae muscles extend the spine. They are heavily used in stiff-legged dead lifts and dead lifts.

The arms are comprised of the triceps, brachialis, biceps, and forearm muscles (wrist flexors and extensors). The triceps function to straighten or extend the arm at the elbow. The brachialis flexes or bends the arm at the elbow with the hand in pronation (facing in or forward) as when performing a hammer curl or a reverse curl. The biceps flex or bend the arm at the elbow with the hand in supination (facing backward) as when performing a barbell or dumbbell curl.

The abdominal muscles include the rectus abdominus located centrally between the lower ribs and the pubic bone and the oblique muscles located on either side of the rectus abdominus The rectus abdominus performs flexion of the spine (a crunching type of movement that brings the chest toward the pelvis). The obliques also perform flexion of the spine when contracted bilaterally. When contracted unilaterally, they laterally flex the spine (bend the spine to the side) and rotate or twist the trunk as when performing an oblique crunch.

The main muscle groups of the legs or lower body include the quadriceps (quads), hamstrings (hams), the gastrocnemius (gastrocs), and soleus muscles. The quads are comprised of 3 smaller muscles whose primary function is to straighten or extend the leg at the knee and are worked in leg extensions and squats. One of the quad muscles also assists in hip flexion or bringing the knee toward the chest. The hamstrings perform 2 major movements: bending the leg at the knee or knee flexion and they also assist in hip extension or pulling the knee away from the chest. The hams are worked with leg curls and assist the glutes and erector spinae muscles in the stiff-legged dead lift and in squats. The gastrocs point the toe with the knee straight and are worked in calf raises. The soleus points the toe with the knee bent and is the main muscle involved in seated calf raises.

Detailed information regarding all of the muscles of the body can be found here.