The seated barbell shoulder press increases strength and size of the shoulders. The seated position isolates the shoulders by restricting the use of other muscles to assist with the movement. Keep your back straight throughout the movement. Seated barbell shoulder press works your whole,plus triceps and traps. This is a basic shoulder exercise that works the front and side delts and the triceps. It also works the upper chest and upper back as secondary muscles. This exercise can also be done lowing the barbell to back of the head.