Abstract: Exercise treadmills with stationary, forwardly placed supporting surface engaging foot means of fixed form and with rearwardly placed supporting surface engaging support means which are movable relative to the frame of the treadmill to change the angular relation of the frame and the treadmill tread belt relative to the supporting surface. The change in incline of the treadmill tread belt is by either electrical power means involving an extensible jack mechanism or by manually operable means including a gas cylinder with an extensible piston rod movable by gas flow within the cylinder which is in turn controlled by manually operable valve means. When gas can flow within the cylinder, change in incline of the treadmill tread belt is accomplished by the treadmill user moving relatively forwardly or rearwardly on the treadmill belt.