Stand with your feet hip-width apart, knees soft. Dip into a quarter squat, swing your arms, and jump as high as you can - driving both knees up toward your chest at the top of the jump - then extend your legs back down and land softly on the balls of your feet, knees bending deep to absorb it. Reset your balance, then go again. Height first, tuck second: the knees come to you at the top, you don't fold forward to meet them.

Works: quads, glutes, calves, hip flexors, core

Breathing: Exhale explosively on the jump, inhale as you land and reset.

Common Mistakes: Hunching the chest down toward the knees instead of lifting the knees up, landing stiff-legged, and chaining fast, low reps where the tuck never really happens.

Make Easier: Jump lower and tuck less - or split the skill into its parts with Jump Squats for the jump and High Knees for the knee drive.

Make Harder: Chain reps with no reset between landings, pulling the knees to chest height on every jump, or move on to Jumping Lunges.