Static and dynamic forward stability of occupied wheelchairs: influence of elevated footrests and forward stabilizers

With 20 able-bodied subjects, three hypotheses were tested: (1) that elevating the footrests reduces the forward stability of occupied wheelchairs, (2) that placing simulated plaster casts on the occupant's legs further reduces stability, and (3) that forward stabilizers limit the extent of dynamic forward instability. Static stability was studied on a tilting platform; dynamic stability was tested by having subjects descend a ramp. Elevating one or both footrests and adding one or two simulated casts each significantly reduced static forward stability. During dynamic testing with lowered footrests, only seven subjects tipped forward, and the extent of tip was limited by the footrests. With both footrests elevated, eight subjects tipped transiently, and 12 continued to tip until the footrests hit the floor. With the addition of simulated casts, all 20 subjects tipped fully. Elevating one footrest (with or without a cast) caused only transient tips. On a high-friction floor surface, 19 and 18 subjects (with and without casts) experienced full tips or yawing falls to the side of the elevated footrest. The addition of forward stabilizers prevented wheelchairs from full tips or falls, when the users had both legs elevated, or when one of the users' legs (p less than 0.005), was elevated while located on a high friction floor (p less than 0.005). These findings have implications for wheelchair design and prescription.