A flywheel has no weight stack and no plates. It stores the energy you put into it on the way up and hands it straight back on the way down, so the harder you pull, the harder you have to brake. That simple property is why flywheel (isoinertial) training has moved from European Space Agency bed-rest studies into elite football clubs, rehab clinics and, increasingly, commercial gyms. The marketing claim is "eccentric overload": more load in the lowering phase than gravity-bas