A guideline for the design of a four-wheeled walker.

More people use assistive technology devices to compensate for mobility impairments than for any other general type of impairment. Increasing numbers of people with mobility or balance problems use walkers with four wheels. Four-wheeled walkers are often outfitted with seats to make it possible to travel longer distances with intermediate resting periods. The dangers of sitting on a parked walker are well known. Many physiotherapists tell walker users to park the walker against a wall to prevent injury in case the user forgets to apply the brakes or the brakes fail. To design a safer walker that can be used for sitting, the demands placed on it must be measured. With these data, three modes of walker instability must be considered: first, the brakes may hold but the wheels may slide along the ground; second, the entire walker may tip over; and third, the brakes may fail to hold the wheels in place, and they may begin to roll. Mathematical models can be constructed to simulate how different walker designs will perform. By this process, design improvements can be made for existing walkers, and future walker designs can also be proposed.