Start standing next to a 6 to 10-inch high box. Place one foot flat on the box and the other on the ground next to the box—as if you were going to go up a flight of stairs. Next, push down through the box and jump up using only the leg on the box. Drive your arms up as you jump for more height. Switch legs in mid-air and land on the opposite foot. Without pausing, immediately repeat for prescribed number of reps.