A gradient adjusting structure of a treadmill includes two symmetrical adjusting members and a telescopic rod. The dynamic brake avoids backlash, due to counter rotation. The control signal is configured to cause the actuator to output a haptic effect associated with the event. The waste is treated in the reactor substantially without agitation, and a sufficient amount of oxygen, moisture andor nutrients is added into the waste material. Such extension members include straight extensions, L-shaped extensions, and extension with two elements at an acute angle to one another.