I was curious when Vybarr Cregan-Reid said that treadmills were initially designed as a form of punishment. So I looked it up. Yes, indeed.

Treadmills Were Meant to Be Atonement Machines, JSTOR, May 2018
America’s favorite piece of workout equipment was developed as a device for forced labor in British prisons. It was banned as cruel and inhumane by 1900.

Two hundred years ago, the treadmill was invented in England as a prison rehabilitation device. It was meant to cause the incarcerated to suffer and learn from their sweat. It would mill a bit of corn or pump some water as a bonus.
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Most treadmills soon included partitions so convicts could not socialize. They slogged for 10 hours a day in summer, and a mere seven in winter.
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The partitioned treadmill delivered on both fronts. The long hours on it were mind-numbingly boring and physically exhausting. But it soon began to be used less as a work machine than as a torture device. “At first it was used to grind corn or pump water, or as a means of exercise. But it soon became a mere method of punishment, ‘grinding air,’” Henriques writes.
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The likes of Oscar Wilde, imprisoned for gross indecency, worked the treadmill.
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The act of 1898 [in Britain] called for an end to their use.
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The treadmill came to America in 1822. … But, by 1827, the mills had fallen into only sporadic use.
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In the 1960s, the American mechanical engineer William Staub created a home fitness machine called the PaceMaster 600. He began manufacturing home treadmills in New Jersey. … Now, it’s the top selling piece of exercise equipment in the U.S.