Pushups provide a great multi-muscle workout, but they can't hit everything. The main target of the pushup is the pecs, both the sternal portion -- the muscles that lift your breasts -- and the clavicular portion -- the muscles under the collar bone that make you look great in a v-neck. Pushups also work your triceps and your anterior, or front, deltoids. They do not work your biceps.
Biceps in Pushups
Try to keep your eyes open for this one. The target muscle of any exercise is the main muscle worked, but some exercises work additional muscles as synergists, or assisters. When done in standard form, that is, with your body in a plank -- or on your hands and knees -- and your hands placed just slightly more than shoulder-width apart, your triceps and front deltoids, as assisters, also have to contract and expand. The biceps only act as a dynamic stabilizer, which means the length of the muscle doesn't really change throughout the exercise, and the effect on the muscle is pretty much nil. In addition, it's only the short head, or inner part, of the biceps that is involved at all.
Hand Placement
Hand placement further affects how much work each muscle gets. Placing your hands farther apart works the pecs even more. However, the closer you place your hands, the more work your triceps will have to do in lifting your body weight. Placing your hands together so that your index fingers and thumbs form a triangle will transform an ordinary pushup into a triceps killer.
Other Pec Workouts
Pretty much the same applies to the majority of pecs exercises. Machine presses, chest presses, dumbbell presses and chest dips all work the triceps rather than the biceps. The rare exceptions are flyes when done lying flat or on an incline or seated with a cable. These exercises work the short head of the biceps slightly, as assisters, and won't work the triceps at all. However, standing flyes done with cables do not work the biceps or the triceps.
Working Other Muscles
So if you're doing pushups, you'll need to come up with other exercises for your biceps, like dumbbell, barbell or preacher curls. It's also important to work your posterior, or back, deltoids, unless you want to look like Quasimodo. OK, it probably won't be that bad, but working the pecs and neglecting the posterior deltoids is a common mistake that leads to so many rounded shoulders -- that and sitting at a computer all day. Incorporate exercises like reverse flyes or seated rows into your regimen, making sure to squeeze your shoulder blades together at the top of the move.
