The Arnold press is a killer upper body move. It will tone and strengthen your deltoids (the triangular muscles on top of your shoulders). And because the Arnold press involves moving in multiple planes of motion, you'll get the benefit of targeting several areas of the muscles involved instead of just one.

Is Arnold press harder than shoulder press?

Is Arnold press harder? Yes, both technique and pushing against same resistance (weight) is more difficult. However don't mistake it for being more effective in building your shoulders.

Why Arnold press is bad?

Don't Over-Rotate

Eb says: The Arnold press is a great move for hitting the shoulder all-around, but, as its generally done, it does place your shoulder at slight injury risk. You're rotating into internal rotation as you press up, a combination that can potentially limit the joint space between humerus and clavicle.