Although the term "press" often refers to a chest exercise, it can also refer to other pressing movements, such as those for the shoulders or triceps. The military barbell press, an overhead pressing movement, targets several muscles of the upper body, but the chest is not one of them.
A loaded barbell provides resistance for this press. The exact definition of a military press is fuzzy. It is often considered an alternative name for an overhead shoulder press, with the two exercises being the same. But some authorities distinguish the two movements by foot stance -- an overhead press has a hip-width stance and a military press places the feet together. Regardless of the stance, the execution of the movement is the same. Hold the barbell in front of your chest with an overhand grip and press it overhead until your arms are straight. Slowly lower the bar back to your chest.
The military barbell press mainly works the shoulder, or deltoid, muscles. The anterior deltoid, the front head of the shoulder muscle, does much of the work. The side, or lateral, deltoid and the rear, or posterior, deltoid are also involved in the movement, although to a lesser degree than the anterior deltoid.
Secondary movers include synergists -- muscles that assist the main movers -- and stabilizers -- muscles that help stabilize the body as you perform the movement. The pectoralis major, or main chest muscle, is not a primary mover during the military barbell press, but the clavicular head of the pectoralis major does assist. The clavicular head is the smaller head of the chest muscle; it sits above the larger, more prominent, sternal head. The triceps and traps also assist the shoulders during the military press exercise. The traps and biceps act as stabilizers. If you perform the exercise standing, the muscles of the low back and abdomen also help stabilize your torso as you press the weight.
If you perform the military barbell press with your feet together, this creates more of a balance challenge since you do not have a wide foundation. Start with light weight and gradually increase the weight over time.
Although the standing press activates more stabilizer muscles, the seated version discourages cheating because you cannot arch your back or use your legs to create momentum. The behind-the-neck version of the shoulder press exercise is not recommended, given the stress this position places on the small and fragile rotator cuff muscles of the shoulder.