 An ill-fitting seating system can increase tone, since any noxious stimuli, such as irritation or pressure, can trigger hypertonicity.Additionally, repeated extensor thrusts against rigid chair parts can result in breakages in the wheelchair or adaptive seating.A seat and/or backrest that moves dynamically can accommodate involuntary extensor thrusts, absorb the extensor tone and, through the movement of the seating system, dampen the overall impact of hypertonia on the body.