HOW: Stand on the step. Shift all of your weight to one leg. With the foot in the air, you will reach forward and lightly tap the ground with your heel, and then come back up to your starting position.
FEEL: You should feel all the thigh muscles and the butt muscles working in the leg you're standing on, but primarily in the thigh muscles.
COMPENSATION: Avoid putting too much weight (if any weight at all) on the foot you are reaching down with. Don’t let your knee cave in, and avoid rounding your back or side bending.