Which muscle is primarily responsible for extending the arm while performing push-ups?

The triceps muscle is primarily responsible for extending the arm during push-ups. This muscle is located at the back of the upper arm and plays a crucial role in the movement of straightening the elbow. When performing a push-up, as you lower your body towards the ground, the triceps are engaged to control this descent. Then, as you push your body back up to the starting position, the triceps contract forcefully to extend the elbow and lift the body away from the ground.

While other muscles can assist in the movement, particularly during different phases or for stabilization, the triceps are uniquely designed for the primary action of elbow extension that occurs in push-ups. The biceps, for instance, are primarily involved in flexion of the elbow, the deltoid assists with shoulder movements, and the pectoralis major plays a significant role in shoulder flexion and adduction but does not directly extend the elbow. Hence, the triceps are indeed the key muscle that facilitates the extension of the arm in this exercise.