The MedX restraint was not meant to to take out the superficial muscles as McGuff suggests. The restraint was designed to block pelvic rotation and thus contribution of the hip & thigh muscles. ALL of the paravertebral spinal extensors were meant to be activated & contribute to this muail-arttcuilte musculoskeletal SYSTEM of support. As joint angles change,? active insufficiency occurs in certain muscles as extension proceeds, and others take over. The MedX Medical Lumbar tracks this beautifully.