In gym, so much energy is used to on the treadmill, cycling machine and cardio machine. Anyway those energy can be kept?

hmm......put a generator on every machine then can generate electricity...from there anything can be done.
cost wise....not so attractive for development...

Maybe the stored energy can be used to power up the electronics on the gym equipment, like before you start it runs by battery after you start working it will switch to mechanical powered.

there's already such gyms which generate electricity from exercise:
http://ecohearth.com/eco-zine/travel-and-l...-at-a-time.html

I don't see why not. But is it economical? To the owner, how much can he save and how long does it take him to get back his investment?

On the issue of green living, it would be nice to have a treadmill at home. Then motivate your self to generate enough power to light up your house. Any electrican can calculate the killowatt needed? Then perhaps dietician can calculate fat burnt. It may be a good sliming program to help mother nature.

It would be a good motivation to make people be fit too. Imagine if all the work on the threadmill is kept in some generator. The energy can then be connected to a fan to generate energy. If possible, maybe the generators can be sold like batteries.

If for me I would make it a job. Use treadmills to charge an array of batteries and then sell them to a power company.

Reminds me of hamsters running in wheels

Definitely possible. Energy can be changed from one form to another, so the kinetic energy from the moving treadmill can be converted to electricity. Just like a dynamo

kinetic energy.. energy from one form to the other. Yes, it can be done. Your question is answered.

1. Rig the treadmill to a device that will charge a battery. Then you can carry that battery anywhere as a portable power supply.

2. Rig the treadmill to a wheel that winds up a powerful coil spring (like alarm clock spring). You can bring that wound-up spring anywhere, hook it with something that will convert rotational energy to whatever energy and then toinnggg... release the spring's pin to unlock the energy.

The energy conserved by either method is not 100%. You'll lose 30-40% in the storage conversion process I think.