Abstract: A passive treadmill having a governor mounted upon one end of a treadmill roller to adjustably limit the rate of speed of the treadmill belt. Resilient flexible rotating springs flex due to the centrifugal force developed during rotation, the magnitude of the centrifugal force being a function of the linear speed of the treadmill belt. Arcuate shaped brake pads mounted on integral projections of the flexible springs move into sliding engagement with an annular stationary surface to limit the linear speed of the treadmill belt. A rotatably mounted cam is manually adjustable to adjust the spacing between the aforesaid slidably engagable surfaces to adjust the operating speed. A stabilizing ring arranged between the governor springs prevents the projections from resonant non-uniform flexing.Support rollers rollingly support the treadmill belt, and are rotatably mounted within elongated openings provided in each of a pair of mounting rails.