Push-ups and pull-ups persist as workout staples for a reason: They effectively train just about every muscle in the upper body. They are also functional. You're more likely to move your body weight around than a fixed bar or pulley machine. Use push-ups and pull-ups alone to create a strong upper body, or include them as part of a total upper-body training routine that builds practical strength for sports and everyday life.
Start with the Back
You include pull-ups in a back workout for good reason. The primary muscle worked is the latissimus dorsi -- the broad back muscle that covers the backs of your ribs. The rhomboid and trapezius muscles of the upper and middle back activate to assist the lats in the pulling movement.
Don't Stop There
The act of pulling up your own body weight requires assistance from multiple other muscles in your upper body. Your shoulders -- especially the posterior deltoids and the muscles that make up the rotator cuff -- are essential in completing a pull-up. The biceps, muscles of the forearm and even your hand muscles help as you grip the bar and heave yourself up. Even the chest assists. Pullups activate the small pectoralis minor that lies underneath the larger pectoralis major.
Balance It Out
Pull-ups mainly target the back side of the upper body, so add push-ups, which primarily target the front side, to create balance. A balanced body is less vulnerable to injury and looks symmetrical. The major muscles worked by push-ups include the pectoralis major -- the large, fanlike chest muscle -- the anterior deltoids and the triceps. These are muscles mostly neglected by the pull-up, although the triceps do stabilize the elbow joint as you draw your body up and down.
In addition to most of the major muscles in the upper body and many of the minor ones, push-ups and pull-ups both work your core. During push-ups, your abdominals and the erector spinae along the vertebrae work to keep your hips from sagging. When you do pull-ups, your abs engage to prevent wild swinging of the body as you hang in space. Although full push-ups and pull-ups are challenging, they aren't out of reach for even beginning exercisers. Do push-ups with your knees on a mat at first and work up to the full version. For pull-ups, use an assisted pull-up machine or have a spotter hold your legs to help you get up and over the bar.