The pectoralis major has two heads: the sternocostal head and the clavicular head. These two heads help you move your arms in different directions, and as one head contracts, the other relaxes.

A. Injuries to the chest muscle known as the Pectoralis Major, which allows you to reach strongly across your body, are quite common in weightlifters and football players.

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Of course, the primary reason most people do push-ups is to tone and build muscle. "Push-ups are a multi-joint exercise, requiring movement at more than one joint at a time," explains McDonough.