A machine with a moving belt surface where you can walk or run in place while staying in one spot, used for exercise.
From 'tread' (to step on) plus 'mill' (a wheel or device that grinds). Originally, treadmills were wheels powered by animals or people walking to grind grain, then were adapted for exercise.
The first treadmills weren't exercise equipment—they were torture devices and punishment mechanisms in prisons and military camps, where condemned people had to walk on them to power machinery.
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