content: "A typical treadmill shift lasted eight hours. Workers spent 40 percent of that time resting. That's a lot worse than it sounds. It meant raising the lower half of their bodies 11,000 feet per day. And yet, hard as it was, 200 men and women could hardly match the output of one water wheel....For a while Charleston slave-owners could rent one to punish runaway slaves. But labor was too precious to waste that way in an expanding land. We preferred to let prisoners do ugly jobs that had some purpose -- picking cotton, or breaking rock. Cubitt's treadmill may have originally had a productive purpose. But a pound of coal could soon do the work of five men working all day on a treadmill."  https://www.uh.edu/engines/epi374.htm