These are pretty self-explanatory, but mind your technique. "I keep my back straight and squat down till my open hands touch the outside of both calves," Rutten explains. "Then I explode upward, land softly, and right away repeat. I never rest in between reps, only in between sets."
Another more expert variation is to try to tuck your knees into your chest in the air during each jump. Bas suggests going for sets of 20, but as with any exercise, your goal is to try to break your numbers every time.