The constant thud under your feet, the cramped space, and the endless monotony of going nowhere. You glance at the clock and realize it’s only been eleven minutes. “Why am I doing this to myself?” you wonder. Strangely enough, treadmills were actually designed to be a form of punishment.

Back in the 1800s, the English prison system was atrocious. Execution and deportation were common, and those in jail lived in appalling conditions. Religious groups, philanthropies, and notable figures like Charles Dickens pushed for prison reform. They succeeded, leading to remodeled prisons and new rehabilitation methods, including the treadmill.

Sir William Cubitt, an English engineer, invented the original treadmill in 1818. Prisoners had to step on 24 spokes of a large paddle wheel. As it turned, they either kept stepping up or risked falling off, much like modern stepper machines. The wheel’s rotation powered mills, pumped water, and crushed grain, giving the treadmill its name. It seemed like a win-win—getting prisoners in shape while helping rebuild Britain’s economy, which had been hit hard by the Napoleonic Wars. But it was a different story for the prisoners.

On average, prisoners spent six hours a day on treadmills, the equivalent of climbing 5,000 to 14,000 feet, or about halfway up Mount Everest. Imagine doing that five days a week with little food. The idea spread quickly, and within a decade, over 50 prisons in England and a similar number in America had treadmills. The combination of extreme exertion and poor nutrition often led to breakdowns and injuries for prisoners.

Some prison guards, like James Hardie in New York, claimed that the monotonous steadiness of the treadmill was its real terror, not the severity of the exercise. This gruesome practice continued in England until it was banned under the Prison’s Act of 1898 for being too cruel.

Yet, the treadmill made a comeback. In 1911, a treadmill patent was registered in the U.S., and by 1952, the modern version we know today was developed. When jogging became all the rage in the 1970s, the treadmill gained popularity as a convenient way to boost fitness and shed pounds. And let’s admit, it’s pretty effective at that.

So the next time you willingly hop on a treadmill, just be glad you can decide when to step off.