This movement is used to build mass in your quads while working stabilizer muscles in your lower legs.
Begin by placing a bar across your back, just as if you were performing a squat. Next, stand in front a flat bench that will support your weight. Begin by placing one of your feet onto the bench and raise your body by pushing through your heel. Next, place the foot of your opposite leg onto the bench. Step down by returning your second foot back to the ground. Then lower your body and bring your initial foot back to the floor. Repeat with this leg until you complete the set number of repetitions and then repeat with the opposite leg for the same amount of repetitions.
This movement is easier on the lower back then other exercises, because you use one leg at a time with lighter weights.
This movement can be performed with dumbbells; this is a better choice if you have balance problems.