Long associated with development of upper-body strength, push-ups are considered a useful way of exercising the chest muscles, particularly the pectoralis major, but also the triceps in the upper arm and the anterior deltoids in the shoulders. All of this assumes, of course, that the push-ups are being performed correctly, which involves keeping the back rigid, which can add the benefit of strengthening the back muscles and, of particular importance, the lower abdominal muscles, which are the core of much of the body’s aggregate strength. It cannot be emphasized enough, however, that push-ups must be done properly in order to maximize their potential for adding strength to those muscle groups.
There are a number of variations to the standard push-up that exercise additional muscles, particularly in the lower chest area, but by and large the main upper body muscles are those that benefit the most from all types of push-ups. In conclusion, then, muscles are strengthened through the performance of push-ups. Such strengthening, however, will not extend to building muscle mass to any noticeable degree, for which purpose weight-training is generally required.