These old fashioned means of powering agricultural equipment like mills, drainage channels, raising water and more were described using the term treadwheels. Sometimes the human or animal would power the wheel from the center and sometimes the outside of the wheel. They were quite complex and show an advanced technological civilisation to design.
Treadwheels were also used as punishment for criminals in prison. Often the prison treadwheels didn't power anything at all and were forced labor. They would make the prisoner tired and less likely to revolt or commit a crime again. There could be 10 men in a row stepping on the wheel like never ending stairs while prison officers look on.
The prison treadwheels typically had wooden partition between each man so they couldn't communicate with each other. They would power the wheel for 6 hours a day and take a 5 minute break after 15 minutes of work. This was banned in 1902 in Britain as a form of punishment due to forced labor. The US tried the wheel briefly but it was never widely used.
The term treadmill wasn't widely used
The first patent for what we would recognize as a treadmill was in 1913 and they called it a "training machine". This never caught on immediately as the design for the patent was complicated and not easily replicated. It was in 1968 when Dr Kenneth Cooper wrote a book called "Aerobics" that changed everything.
This book "Aerobics" changed the way of thinking and encouraged the masses to exercise aerobically or in a way that improved cardiovascular fitness. People started running when they read the health benefits that could be had with this form of exercise. There was a demand for being able to do this aerobic exercise in the home. William Staub had the first design for a treadmill inspired by the book and he called his consumer treadmill the "PaceMaster 600".
After many tries and failures William Staub and Dr Kenneth Cooper who wrote the popular exercise book, approached a fitness equipment manufacturer. This was to build treadmills suitable for the home. The term treadmill was used to combine the milling that was used in the past, but not treadwheels. One can only assume the penal use didn't favor the term "treadwheel".
So treadmills have been known as treadmills ever since. Not as a punishment but as exercise machines that have become popular worldwide. They are far simpler to make than the earlier ones and have the latest technologies attached to them. The basic part of the belt with 2 rollers and a deck has been around for many years.
You can still find treadmills everywhere. Especially for rehabilitation in people as well as animals after injury. You have some filled with water up to the waist to help you walk or run without having any impact and building muscle. Dogs and cats can be helped in recovery with their very own treadmills in advanced veterinary centers. Treadmills will be around for years to come.