Starting position: Begin on your hands and knees, arms straight; your hands slightly wider than shoulder width. Extend and raise your right leg behind you, keeping it straight, toe about a foot from the floor. The key is to keep arms straight and back flat. This is the beginning of a circuit, where you add on a new move with each progression.
Target muscles: Core, butt, pectoralis major (chest), and triceps (underside of upper arms).