Why can’t we ‘recycle’ energy ? (Say, generate electricity from gyms)

If recycling is environmentally friendly, then why haven’t we thought seriously about recycling the world’s most important resource i.e. energy.¬†For example, the amount of energy expended in gyms across the world is phenomenal. Gyms consume a lot of energy because they have they keep their electrical equipment running (treadmills, ellipticals etc.), but the amount of energy expended on these machines is probably more than the amount of energy consumes (if there is any means to compare equivalence).

Can’t we figure out a way to convert the physical motion into electro-mechanical energy that can somehow be converted to electrical impulses and ‘generate’ energy that can be utilized by consumers? Might be a long stretch to make this feasible in ¬†terms of cost and implementation, but the potential gains warrant enough research to be put into this effort. This is a thought that has intrigued me for many many years now, since I first started going to a gym. I just feel that the energy we expend can somehow be ‘recycled’ and channeled back, and that can potentially lead to a golden age of ‘recycled’ energy!!