Start in a push-up position with your hands under your shoulders. Lower onto one forearm, then the other, so you're in a forearm plank, then press back up one hand at a time to straight arms. Alternate which arm leads on every rep. Your hips will lobby hard to sway with each transition - the exercise is keeping them level and quiet while your arms rebuild the plank underneath you, over and over.

Works: triceps, shoulders, core, chest

Breathing: Inhale as you lower to the forearms, exhale as you press back up.

Common Mistakes: Rocking the hips side to side through the transitions, always leading with the same arm, and placing the hands too far forward to press back up efficiently.

Make Easier: Do them from your knees, slow down and reset between reps, or build stability first with Shoulder Taps.

Make Harder: Bring your feet together and slow every transition down, or move on to Push-Ups - Close Grip to press the same muscles through a full range.