Hollow Body Press

Lie on your back and press your lower back flat into the floor by drawing your ribs down and your belly button in. From there, lift your shoulders and legs slightly off the ground, arms reaching overhead and legs straight, so your body forms a shallow, banana-like curve with only your lower back and hips touching down. The lower your arms and legs hover, the harder your core has to work to keep your back pinned to the floor -- if your lower back arches up, you've dropped too low for your current strength; lift your legs higher until it stays flat. Keep breathing steadily through the hold rather than bracing your breath away.