damn. i just saw the same idea posted by someone else about 3 minutes after i posted it.

That is a great idea. Apparently this is already being done in Europe. Check this out:http://greenlivingideas.com/health-and-fitness/green-gyms.html

If was cost effective then this idea should be utilized in more areas then just a gym. Unfortunatly the cost of replacing excisting machines with energy producing ones in current gyms are not logical. I know I would rather by a energy producing treadmil or bike machine if given the option.

http://www.thegreenmicrogym.com/

I can see getting energy out of a bike or eliptical, but people don't walk on non-powered treadmills anymore. Treadmills use more energy, they don't produce it. The older ones that weren't powered had to have a pretty good uphill to keep the belt turning.

I really like the idea of making a "Power Plant Gym". Perhaps, they can even pay YOU for helping supply power. Kind of like what they already do with solar panels. Talk about incentive to hit the gym.

It's a nice thought, but in practice, the amount of power generated won't even pay for the extra equipment needed (transformer etc). Thus it would be a wast of the planets resources to build such a system.

The University of Oregon modified the aerobic machines in their rec center to do this.