To perform a hack squat step onto a hack squat machine and position your back against the machine’s backrest. Place your shoulders under the padded shoulder rests, with your feet about shoulder-width apart on the foot plate. Slowly lower your hips, bending your knees to 90 degrees. Stand up again to return to the starting position. Hack squats target the quadriceps muscles, or quads, on the front of your thigh.