Start in a push-up position with your hands under your shoulders. Punch one fist straight out in front of you at torso height - a real punch, extended fully with the arm snapping out and back - then plant the hand and punch with the other. The faster the fists fly, the harder your core has to work to keep your hips level and your body from twisting: the punches are the engine, the stillness of everything else is the exercise.

Works: abs, obliques, shoulders, arms

Breathing: Sharp exhale with every punch, quick inhale on the switch.

Common Mistakes: Rotating the hips and torso with each punch, punching downward at the floor instead of straight ahead, and letting the hips sag as the set wears on.

Make Easier: Slow the punches down and pause between them, or widen your feet for a broader base - or start with Shoulder Taps.

Make Harder: Drive the punch rate up with the hips locked level, or move on to Plank Arm Raises for slow holds or Push-Up + Jab + Cross for the full combination.