Human Tread Wheel Engines are devices that perform work using the power of humans walking inside a wheel (like a hamster) outside a wheel or along a wheel laying horizonally. In 500 BC Greeks writings describe tread wheel cranes. The Roman Haterii Tomb in 100 AD show a treadwheel crane used for building construction.
The Roman Empire improved on this crane thru the centuries. They used the treadwheel cranes to lift heavy stones when constructing their complex system of aqueducts to bring water into their cities.
An image of an high medieval construction site from the Morgan or Maciejowski Bible around 1250.
In 1330 a Treadwheel was built and still survives at Salisbury Cathedral, Wiltshire England to raise building material while constructing a tower.
Interestingly, the wheel had no breaking mechanism save the strong hands of the men turning it. If something was momentarily dropped, there was no way of keeping it from leaving a crater in the cathedral floor hundreds of feet below.
Treadwheel Crane was used at the Naval Yard from 1667 to 1927. A spar was kept handy for levering against the outer edge of the wheel for some braking. Should the load take command, the men in the wheels would be revolved backwards.
Around 1661 in Nuremberg Germany this image of a man furnishing the power for a grain mill shows how the wheel platform is used. He walks uphill as the gears move a millstone to grind the grain.
Sources: Wikipedia, http://www.harwich-society.co.uk , http://wso.williams.edu/~dredmond/cathedrals/salisbury/