A treadmill was a piece of exercise equipment used by Humans that allowed them to run in place.
History and specifics[]
In 2020, the USS Lewis & Clark was equipped with a treadmill the astronauts could use so their muscles would not atrophy because of the lack of gravity in space. (TOS novel: The Rings of Time)
In 2258 in the Kelvin timeline, Cadet James T. Kirk and a Betelgeusian exercised on treadmills in a Starfleet Academy gym. (SA - Starfleet Academy comic: "Issue 2")