Lie supine on sled with shoulders against pad and place feet on platform. Grasp handles to sides and straighten knees. Place toes and balls of feet on lower portion of platform with heels and arches extending off.
Push sled up away from platform by extending ankles as far as possible. Return by bending ankles until calves are stretched. Repeat.
Not all Hack Squat machines have platform with opened lower end allowing for this movement, but some platforms may accommodate calf block, see example. Disengage docking lever if it impedes movements. Keep knees straight throughout exercise or bend knees slightly only during stretch. Quadriceps serve as synergist muscle if knees are bent slightly during stretch. See Calf Exercise Analyses.