The treadmill gets its name from exactly what it sounds like: a device you tread on that powers a mill. The original treadmills weren’t exercise equipment. They were large machines, often found in prisons, where people walked endlessly to grind grain or pump water. The “tread” referred to the stepping motion, and the “mill” referred to the grinding work that stepping produced.
From Treadwheel to Treadmill
The earliest versions of these devices were actually called treadwheels. Picture a wide, hollow cylinder made of wooden steps built around an iron frame, almost like a giant hamster wheel. People (or sometimes animals) would walk on the outside of the wheel, and their body weight would cause it to rotate. That rotation could be harnessed to crush grain, pump water, or perform other mechanical work.
The name shifted from “treadwheel” to “treadmill” as the grain-grinding function became the device’s most common use. A mill, after all, is any machine that grinds. So a wheel you tread on to power a mill became, simply, a treadmill. The two terms overlapped for decades, but “treadmill” is the one that stuck in everyday language.
The Prison Treadmill That Made the Name Famous
The word “treadmill” became widely known thanks to British prisons. In 1818, a civil engineer named Sir William Cubitt designed a large treadwheel specifically to keep convicts busy. The idea was that idle prisoners should be put to useful labor, and forcing them to walk on a rotating cylinder for hours seemed like the perfect solution.
Cubitt’s design was a massive device. Some versions could handle as many as 40 prisoners at once, all lined up along a wide cylinder, stepping on wooden planks in an endless climbing motion. As the cylinder rotated under their feet, each prisoner had no choice but to keep stepping or risk falling. The power generated was sometimes connected to a grain mill or water pump. In other prisons, the treadmill wasn’t connected to anything at all. Prisoners simply walked for hours as pure punishment, producing no useful work whatsoever.
These prison treadmills spread across Britain and its colonies throughout the 1800s. Prisoners could spend six or more hours a day on them, climbing the equivalent of thousands of feet. The monotony and physical exhaustion were the entire point. A series of prison reform acts throughout the 19th century gradually restricted how long inmates could be forced to walk, and the Prison Act of 1898 finally called for an end to their use altogether.
How a Punishment Became a Workout
For nearly a century after prison treadmills were abolished, the word “treadmill” carried grim associations. It was used mostly as a metaphor for tedious, pointless labor. That changed in the late 1960s.
In 1968, Dr. Kenneth Cooper published a book called “Aerobics” that made the case for sustained cardiovascular exercise as a path to better health. The book caught the attention of a mechanical engineer named William Staub, who realized most people had no convenient way to run or walk indoors. Staub built the first affordable home treadmill and sold it under the brand name PaceMaster. His earliest models were simple: wooden rollers, a basic belt, and an on/off switch near the floor. They cost $399 in the 1970s, roughly $2,000 in today’s dollars.
Staub kept the old name. A treadmill was still, mechanically, a surface you tread on that moves beneath your feet. The difference was that modern treadmills are powered by electricity rather than by the walker’s body weight, and the goal flipped entirely. Instead of punishing people with forced walking, the new treadmill invited people to walk or run voluntarily for their own benefit.
Why the Name Still Fits
The word “treadmill” has survived for over 200 years because its literal meaning never stopped being accurate. You tread. The surface mills beneath you. Whether the purpose was grinding grain in a medieval village, punishing prisoners in Victorian England, or burning calories in a modern gym, the basic motion is the same: continuous walking or stepping on a surface that cycles underfoot.
The metaphorical use of the word persists too. When people talk about being “stuck on a treadmill,” they’re echoing the prison version of the device, describing repetitive effort that feels like it goes nowhere. It’s a rare case where a word’s darkest historical meaning and its most common modern use coexist in the same language, separated only by whether you chose to step on.