A polio victim who has been in a negative pressure ventilator ("iron lung") since 1950 was in need of an activated mattress to combat the hallucinatory effects of complete immobilization and to assist with body pressure distribution. A mechanical method was used to give the patient's mattress a moving wave form of vertical amplitude 50mm with a period variable from 50 seconds to infinity. His arms rested on separate supports which oscillated 180 degrees out of phase with the trunk support. The device is powered by a 12 volt electric motor operating through two mechanical reduction gear units. It differs significantly in design and purpose from pneumatic ripple mattresses.