A treadmill assembly that includes a frame and a treadmill belt. In addition, a sensor produces a signal representative of an aspect of the user's position relative to at least one point on the frame. A belt rotation assembly turns the belt with a speed related to the signal. In one preferred embodiment the speed of the belt is inversely proportional to the distance between the user and the front of the treadmill. In another preferred embodiment the treadmill is sized to support a cycle.