sentence: other kinds of resistance machines friction machines spring - loaded machines ( such as bowflex ) fan-loaded machines fluid-loaded machines bullworker hydraulic equipment whole body vibration outdoor gym pneumatic exercise equipment soloflex stretchtrainer endless-path machines the gymnasticon , an early exercise machine resembling a stationary bicycle stationary bicycles exercise bicycle running/walking machines treadmill elliptical trainer elliptical machines ellipticals ( elliptical machines ) are a combination of stair-climbing and a treadmill .