The side plank is a great isometric exercise that engages muscles in your legs, hips, glutes, low back and abdominals. Begin by laying on your side on the floor with legs extended and one foot resting on the other. Bend your arm that is against the floor to a 90-degree angle and prop yourself up on your elbow and forearm. Then lift your hips and legs off the floor so you are just on the lateral edge of one foot. If you are a beginner, try holding this position for 20 seconds. Be sure to breathe steadily during the duration.