HOW: Stand on the step. Shift all of your weight to the leg you want to exercise. With the foot in the air, you will reach back and lightly tap the ground, and then come back up to your starting position.
FEEL: You should feel the thigh muscles and the butt muscles working in the leg you're standing on.
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.