Unpowered treadmill

Unpowered treadmills, that is, treadmills without electric motors, may sound a bit incredible, but they really exist. It does not need to set the speed, but can be adjusted at any time according to the running speed of the exerciser. The faster you run, the faster the speed of the treadmill will naturally be. When you slow down, the speed of treadmill will naturally slow down or even stop.