Start in a push-up position with your hands under your shoulders and your body in a straight line. Drive one knee in toward your chest, then switch legs in the air, extending it back as the other knee comes in - and keep switching in a fast running rhythm. Your hands stay planted, your hips stay low and level, and your core stays braced while your legs do the sprinting.

Works: abs, hip flexors, shoulders, quads

Breathing: Quick and rhythmic, exhaling with each knee drive - find a pattern and hold onto it as the pace climbs.

Common Mistakes: Letting the hips pike up into the air, bouncing the shoulders back behind the hands, and shortening the range until the knees barely move.

Make Easier: Slow it down to a deliberate step-and-switch with both feet touching down - Slow Climbers is exactly that - or elevate your hands on a sturdy surface.

Make Harder: Sprint the tempo while keeping the hips pinned level, or move on to Climber Taps or Plank Jump-Ins.