Position barbell just behind legs. With feet flat on floor, squat down and grasp barbell from behind with overhand grip.
Lift bar by extending hips and knees to full extension. Squat down by bending knees forward while allowing hips to bend back behind, keeping back straight and knees pointed same direction as feet. Descend until thighs are close to parallel to floor and bar is behind lower leg. Repeat.
Throughout lift, keep hips low, shoulders high, arms and back straight. Knees should point same direction as feet throughout movement. See flawed demonstration showing depth of hack squat that is NOT sufficient and knees are NOT pointed same angle as feet. Individuals with short arm to torso ratio or protracted shoulder posture, may find this exercise very difficult to perform. See Squat Analysis.