A motion-based push activation power assist system for manual wheelchairs. The system uses motion-based measurements to determine when the user applies a push to the wheelchair handrims and brakes with the handrims. The push recognition activates a drive system that provides an assistive driving force-pulse to the wheelchair to reduce the demand on the user during propulsion. The brake recognition deactivates the power assist. The provided power assist is proportional to the sensed push and can be modulated to different proportional settings.