Plank Jacks

Get into a plank with your core fully braced and your body in a straight line from head to heels. Your shoulders pack down and back, your glutes squeeze hard, your core stays tight throughout. From here, jump your feet wide and then narrow, side to side, in rapid succession. Each jump is controlled, not sloppy; your hips do not sag or pike up toward the ceiling. Only your legs move; the plank position holds steady. The faster you jump, the more your core has to work to keep you stable and in position. Maintain hollow tension throughout.