Start in a push-up position with your hands under your shoulders. Drive one knee in toward your chest and, as it comes in, reach the opposite hand back to tap your foot - then plant the hand, extend the leg back, and repeat on the other side. Every tap leaves you balanced on one hand and one foot for a moment, so keep your core braced and your hips low and steady through the switch.

Works: abs, obliques, shoulders, hip flexors

Breathing: Exhale on each tap, inhale as you return to the plank - steady rhythm over speed.

Common Mistakes: Piking the hips up to make the tap easier, twisting the whole torso sideways instead of reaching from the shoulder, and rushing so fast the taps miss.

Make Easier: Skip the tap and just drive the knees in - that's Climbers - or slow everything down with Slow Climbers until the balance feels solid.

Make Harder: Pick up the pace while keeping the hips level, or move on to Plank Jump-Ins or Side Plank Rotations.