Logic says the push-up won't build strength unless you're kind of weak to begin with. Its benefits lie elsewhere. "If you do push-ups correctly, you develop your scapular muscles and your rotator-cuff muscles to stabilize your shoulders. If you do bench presses instead of push-ups, you don't have to use those muscles as much," says Michael Clark, C.S.C.S., a physical therapist and president of the National Academy of Sports Medicine. In other words, push-ups not only build up the facade in front of your physique, but also develop the support system behind those muscles, too.
Here's why that's important: In every physical action, some muscles act as the engine and some act as the brakes. If the brakes aren't strong and durable enough to counterbalance the engine, you've got an injury waiting to happen. When a guy comes up with a chronically sore shoulder from bench pressing, for example, the problem is usually that the chest and shoulder muscles are too strong relative to the muscles behind them.
So it makes sense that push-ups help improve muscular balance, which is important for developing serious strength. And with strength comes muscle size.
