HOW: Begin on your hands and knees, with your knees under your hips and your wrists under your shoulders. First push your body away from the floor by spreading your shoulder blades. While staying strong in the shoulder blade lift one hand to tap the opposite shoulder, return to starting position and switch sides.
FEEL: You should feel the muscles on the front of your shoulders in addition to your core working.
COMPENSATIONS: Avoid rotating the body or allowing the shoulder blade to sag.