The humerus is adducted so that the proximal and distal ends of the humerus are on an even line with the shoulders. The palms should be on the ground close to the chest. The wrist must be supinated for the palms to be on the ground. For the arm to get positioned correctly, the supraspinatus and anterior deltoid are used to abduct the arm. When the upper limb is lifted horizontally away from the side, the contracting anterior deltoid muscle provides most of the movement and is said to be the prime mover. When the anterior deltoid is acting, certain nearby muscles are contracting. These are called the synergists. One of the synergists of the anterior deltoid is the supraspinatus because it also abducts the humerus. The muscles are also synergists of the deltoid. The biceps brachii is used to flex the elbow joint and supinates the radio-unlar joint when bending the arm to get into this position. The brachialis, pronator teres, and brachioradialis are all used to extend the elbow joint. The trapezius, rhomboids, and levator scapula are also being used in this step by abducting the scapula. This position is illustrated in the picture below.
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Next, you use the arm muscles to push up your body off of the ground. The humerus is being extended. In this action you are extending the elbow, but be sure not to lock the elbows, just straighten. The elbow is adducted, brought back toward the midline. This process is a concentric movement of the triceps brachii. Although it may seem that the biceps brachii are doing a lot of work, they are not. The biceps do not get hardly any work at all. While pushing the body up off of the ground the triceps brachii get mainly all of the action. The biceps merely get flexed, which does not work the muscle at all, it just moves it. The prime mover of the push up is the triceps brachii and the synergists are the corachobrachialis and the pectoralis major.
