Joel Harper demos the superman exercise.

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(Strengthens lower back)

Lie flat on your stomach, reaching your arms overhead with your palms down. Extend your extremities straight out, away from your torso, and lift your arms and legs simultaneously for enough repetitions to cause some muscle fatigue. Look down, and don't overextend your neck. This is about how long you can stretch your body, not how high. Squeeze your butt as you lift. Try to make it to a minute.