Run on the spot, driving each knee up to hip height with every stride - thighs reaching parallel to the floor, landing on the balls of your feet, arms pumping in running rhythm. Stay tall through your torso rather than leaning back to lift the knees, and keep the strides quick and light: it should feel like sprinting in place, not stomping.

Works: hip flexors, quads, calves, core

Breathing: Quick and rhythmic, in time with your stride - find a breathing pattern early and hold it as the pace builds.

Common Mistakes: Leaning back to get the knees higher, landing heavily on flat feet, and letting the knees sink lower and lower as the set goes on.

Make Easier: Slow it to a march - one knee up at a time at walking pace, no impact - and raise the knees only as high as comfortable.

Make Harder: Sprint the tempo with the knees pinned at hip height, or move on to Jump Knee-Tucks or Split Jacks.