The barbell military press is a strict overhead press that uses no leg drive, backward lean or any other body English to make the exercise easier. It is best performed with the bar set in a shoulder-height squat rack so it is easy to get into the correct starting position. To maximize your performance, keep your abs tight, forearms vertical, chest up and exhale as you drive the bar overhead.
The agonists, or primary muscles, used in the barbell military press are the deltoids, or shoulder muscles. You have three deltoid muscles: anterior, medial and posterior, located on the front, side and back of your shoulder, respectively. The military press uses all three deltoids, but the anterior works the hardest. Bodybuilders and athletes perform military presses because they are effective in developing increased deltoid size and strength.
Synergists are helper muscles that, although very active in the performance of an exercise, are secondary to the agonist. There are a variety of synergists in barbell military presses but the most notable are the triceps and upper trapezius muscles. The initial upward drive of the barbell is initiated by the deltoids, but pushing the bar fully overhead is the job of the triceps, which are located on the rear of your upper arm. The upper trapezius, located across your upper back and just below the base of your skull, works hard to pull your shoulder upward as you complete the lift and lock out the bar overhead.
Fixators are stabilizing muscles that hold your joints in position so the agonists and synergists can work as efficiently as possible. As barbell military presses are performed in a standing position, just about every muscle in your body must work hard to keep you upright. However, there are a couple of notable fixators that are more active than others, including the core, or the muscles of your midsection. These muscles must work hard to keep your spine, specifically your lower back, locked in position. A weak core can severely limit the amount of weight you lift overhead. In addition, your rotator cuff, which consists of four small muscles deep within your shoulder joint, must work to keep the head of your humerus securely located in the socket of your shoulder.
Muscles are arranged in pairs across joints. When one muscle contracts, the opposing muscle, which is called the antagonist, must relax to allow uninhibited movement. The antagonist to the deltoids is the latissimus dorsi muscle, which is located on the lateral aspect of your back, directly below your armpit. This muscle relaxes as you press the barbell up and overhead. Overly tight lats can make fully extending your arms more difficult than it should be.