Pick up a pair of dumbbells off the ground using your legs (not your back). Stand with your feet about shoulder-width apart. With your back straight, head up and abs tight, take a large step forward with your right leg and lunge down toward the floor until your left leg is parallel to the ground. Once you reach the bottom, drive your body back up with your right leg until you are in a standing position. Perform the same movement with your left leg and continue alternating until you reach muscular failure.
Tip: It is very important that you maintain proper form at all times when performing this exercise. Make sure to keep your back straight, head up and abs tight throughout the entire movement. Also remember to stay in complete control of the weights rather than using jerky motions or body momentum.