The primary agonist muscles used during a shoulder press are the anterior deltoids and the triceps brachii, while the primary antagonist muscles are the latissimus dorsi and the biceps brachii. Both antagonist and agonist muscles are used for stabilization.
Agonist muscles are the muscles that perform a movement, while antagonist muscles perform the opposite movements. The anterior deltoids are the muscles that run along the front side of the shoulders, and the triceps brachii are the muscles on the outside of the upper arms. During a shoulder press, the anterior deltoids are primarily used during the first half of the movement, while the triceps are primarily used during the second half of the movement to reach lockout. The latissimus dorsi is the large muscle on the upper back, while the biceps brachii are the two muscles on the inner side of the upper arm.