Like many strength-training exercises, the military press and behind the neck press resemble one another in basic execution and purpose, but they have slight differences in exercise technique. Although the technique distinction is small, it renders the military press a safer option for many lifters.
Stand and hold a barbell with an overhand grip just beyond your shoulders. For the behind the neck press, position the barbell across your upper back, behind your neck. For the military press, position the barbell in front of your upper chest. Exhale and press the barbell overhead, extending your arms. Pause for a count, inhale and slowly lower the bar back to the starting position.
The anterior, or front, shoulder muscles are the primary movers for both exercises and the lateral, or side, shoulder muscles assist. However, during the military press, the clavicular head of the chest muscle, which is a small portion of the chest that sits near the clavicle bone, assists more than the side shoulder muscles because of the front position of the barbell. The upper chest is not involved in the behind the neck press. The triceps and trapezius muscles also assist during both movements.
Both exercises can be performed sitting or standing. A sitting position makes it more difficult to cheat and use your hips or lower back to help press the weight up. A barbell is most commonly used for the behind the neck and military press, but you can also use a Smith machine, cable machine or plate-loaded machine.
The behind the neck press is generally considered a contraindicated exercise as it provides no real training advantages over the military press and increases your risk of injury to the neck and shoulders. The position of the barbell places your shoulders in extreme external rotation and abduction. Pressing weight in this position puts a lot stress on the shoulder joints and ligaments. To avoid hitting the back of your head with the barbell, the behind the neck press forces your neck in an unnatural forward position, which increases your risk of neck injury.