A Sit on edge of step with hands just outside of hips, legs bent at about 90 degrees, feet flexed. Lift hips off the edge, pressing shoulders down, and walk feet out slightly further away from step.
B Bend elbows and lower hips as left thigh lifts to chest (knee stays bent at 90 degrees), keeping back close to the step. Extend arms and lower left leg to return to starting position. Do the prescribed number of reps, moving quickly and alternating legs each time. Make it easier by keeping feet closer to the step, harder by walking them further out.