Push ups primarily work the upper body muscles, with some core muscles being worked by providing secondary support. The main muscles worked in the traditional push up are the shoulder (deltoids), chest (pectorals) and triceps. There are many variations that you can use to spice up a push up routine and target specific muscle groups. Hand placement variations in push ups are one way to add variety. Placing your hands wider than your shoulders will work chest muscles more. The diamond hand position works the triceps. You do the diamond by placing the thumb and forefingers of both hands together in a diamond shape with your hands flat on the ground. Foot placement has a huge impact on the level of challenge with push ups.