Hold a 5- to 8-pound dumbbell in each hand, and place left foot on a step or low bench. Take a big step back with right leg (at least three feet behind you) as you bend left knee to a 90-degree angle, as shown. Straighten left leg as you bring right leg forward, and touch step with right foot. Perform 8 to 12 repetitions, then switch legs. To increase difficulty: Lift back knee instead of touching step.