If you’ve ever used a treadmill, you know they can get old fast. They are tiring and quite frankly boring as you don’t physically travel. This is because they weren’t first invented for exercise. In fact, part of their original purpose was to punish prisoners through hard labor.

According to The New York Times, the treadmill was popularized in Victorian Britain in 1917 when Sir William Cubitt designed a machine that was originally called the “Tread-Wheel.” When he designed the machine, he wanted them to be used in houses of correction and penitentiaries. The design was inspired by the water wheels of ancient Greece. Prisoners would have to synchronously step up the stepping boards on the wheel in order to avoid falling off as some were often rather high up. If a failure to keep up occurred, injuries were a possibility. The wheel’s purpose was also to either pump water or grind up grain. This is how it got the name “treadmill.”

Despite the intent of the mills to humanely rehabilitate criminals, the treatment of prisoners was rather poor. In some cases, prisoners were forced to stay on the mill for six to eight hours straight. Oscar Wilde, who had spent two years in a prison with a treadmill, wrote in a poem about his experience “We banged the tins, and bawled the hymns, /And sweated on the mill: /But in the heart of every man /Terror was lying still.” Because of multiple casualties on the treadmills, by the early 1900’s they had been mostly banned in both the United States and the United Kingdom. However, treadmills would soon make a comeback.

According to the CDC, deaths from heart disease were increasing rapidly from the 1920s to the 1960s. To combat this, engineers and cardiovascular doctors developed devices derived from the original treadmill that would increase heart rate and diminish the likelihood of dying from heart disease. In 1939, John Richards made a treadmill marketed towards dog owners in apartments, so their dogs could get more exercise and thus, live longer. Life Fitness states that it was in 1952 that the first modern treadmill for humans was made. Dr. Robert Bruce of the University of Washington and Wayne Quinton added an adjustable motor to Josh Richards’ treadmill. By adjusting the speed of the treadmill, they learned how the beating patterns of hearts could determine victims of heart attack as well as people that are at risk for heart attack or other cardiovascular diseases. This same process is still used today and is known as treadmill-based cardiac stress tests. Bill Staub and Dr. Kenneth Cooper were the first to capitalize on the treadmills as a tool for exercise. In 1968 they began the aerobics movement, of which the treadmill was a big part.

Now, according to Statista, as of 2017, there are nearly 21 million treadmill users in the U.S. alone. The device went from being used as a form of punishment to being one of the most popular exercise devices today. The treadmill is a great example of how much the meaning and purpose of an object can change over time (Related: experience the modern treadmill with a gym membership).