A variation of the Plank, you begin this in the same position as the original. Once lying flat on your stomach, roll onto your left side keeping your body supported by your left forearm. Your hips should be aligned, your right foot on top of the left, your body raised from the floor. As with the Plank you should remain rigid but this time on your side. Hold this plank position steady for five seconds then lower yourself slowly and repeat on the other side.