Position your body in the hack squat machine by placing your feet about shoulder-width apart in the center of the platform. Keep your back and shoulders resting firmly against the pad at all times and point your toes slightly outward. Press the weight up with your legs and remove the stoppers. With your abs tight and head up, lower the weight down until your thighs are at least parallel to the platform. When you reach the bottom, drive the weight back up over the same path until you are in a standing position, but do not lock your knees out at the top. When you have completed your set, stand upright and put the stoppers back in place.
Tip: Make sure that you never lock your knees out when you are in the standing position as this will place undo stress on your knee joints and will also maximize the stimulation of your thigh muscles. Also remember to maintain proper form by keeping your back flat against the pad, head up and abs tight to support your spine.