TRX Mountain Climber

Your feet sit in the straps instead of the floor, hanging just above the ground while your hands support you in a plank underneath the anchor point. Drive one knee toward your chest and let the strap swing it back out, then switch legs. The suspended feet add a wobble the floor version doesn't have, so your core works overtime just to keep your hips from swaying side to side. Keep your hands under your shoulders and your hips level with your shoulders throughout. If your hips sag or pike up, slow down until you can control the strap instead of fighting it.