Muscles Involved: glutes, abs, quads
Exercise Description: Stand with your feet a hip-width separately with your knees slightly bent and your arms hanging straight at your sides. Using your lower abs and the muscles in your glutes and quads, jump off both feet and bring your knees up in front of your chest so you can grab them, as though you were doing a cannonball dive in midair. While in midair, release your knees and land, on soft knees, back to the beginning position. Repeat the exercise.
Useful tips and variations: Keep your eyes focused forward to keep your back in the suitable position. Keep your knees somewhat bent when landing.