[Lewis Thomson (OP)]

Paul is looking for answers to this question from the Naked Scientists.

"With the ocean wind farms why don't they have floating coils of wire surrounding the uprights generating extra power or is there not enough variance in water level where these wind farms are sited to generate any extra power?

Why are not gymnasiums hooked up to the national grid so that folk using exercycles can be generating power? Waste not, want not."

What do you think? Discuss in the comments below...

[alancalverd]

It's worthwhile hooking an exercise bike up to a computer game, so you can waste your life twice as efficiently, but the maximum  human continuous power output is trivial - maybe 50 - 75W for the average gym-goer. As Wikipedia says

While attempts have been made to fit electric generators to exercise equipment, the energy collected is of low value compared to the cost of the conversion equipment.

At current gas prices you'd be hard pushed to save more than 2p per hour with a bike

[Janus]

Look at it this way:  During a typical workout on a machine, you are unlikely to generate enough energy to heat the hot water for the shower you'll need afterwards.

[paul cotter]

I would have guessed 100w max but I defer to alancalerd's estimate of 50-75w. Remember this is also quite intermittent unless one can hold a gun to the heads of the participants. Overall not useful.

[evan_au]

I have occasionally hit 600W on an exercise bike.
- I can only keep it up for 1 or 2 seconds before I drop back to a more sustainable 150 Watts.
-  I can't vouch for the accuracy of the measuring equipment!

PS: I do not have the physique of this champion rider!

[alancalverd]

Weightlifters can exceed 1 kW, but only for a few milliseconds!

A lot of work was done on sustained power when people were competing for the Kremer Prizes for manpowered flight: one mile out-and-return with a continuous 180 degree turn, and eventually across the English Channel. It was quickly discovered that it is easier to teach a champion cyclist to fly  than to train a pilot to pedal a bike at 600W, and it is noteworthy that most of the prize records are held by just one cyclist, Bryan Allen.