Shoulder Press Does NOT Work Shoulders

Shoulder press does not always exercise your shoulders. In fact, most people in the gym keep the movement too high to stimulate your deltoids.  Most of the work will be done by your trapezius muscles, specifically your upper trapezius, if you keep the movement above parallel.

The primary action of the middle deltoid is shoulder abduction up to 90 degrees.  In other words, your deltoid is almost completely contracted when your humerus (upper arm) reaches 90 degrees which is about parallel to the floor.  In order for your upper arm to move any higher, the movement has to be completed by the trapezius muscle.

Therefore, lateral raises are a better exercise for stimulating your deltoid while shoulder press above parallel is better for your traps.  However, if you perform the shoulder press through a broader range of motion, one where your upper arm dips down below parallel and also well above parallel, you would have stimulated both the deltoid muscle and the trapezius muscle.  Happy lifting!!