Medievel times saw the treadmill operative as work, powering pumps, grinding corn etc.
In the Victorian age the treadmill was used as punishment, men where put on the treadmill to do work with no outcome at all, I don't think they even produced anything.
Now, we pay to use a treadmill, we even pay for someone to show us how to use them. The treadmill today does not produce energy, it uses energy as it needs to be plugged into something, so someone, somewhere is creating energy to make this one work.
My treadmill will tell me how many calories I am expending per hour, how many calories I have spent so far, how far I haven't run so far. I wish it would tell me something useful, like calories measured in terms of fractions of a Mars bars (or other popular confection).
Whilst using my treadmill I have tried to use the time even more productivily (other than losing weight) by listening to Rob Bell sermons (downloaded by my lovely wife, and uploaded to my iPod). But I find myself losing concentration and reading the sub titles to Neighbours on the telly screens in front of the treadmills (I must be really shallow).
I bet they didn't have tellys on the Medievel or Victorian treadmills.(or Neighbours)