CNN reports that a company called ReRev is retrofitting gym bikes and elliptical trainers to harness the power of your workout. Thirty minutes on a bike keeps a computer humming for an hour. Okay, this is not the future of renewable energy, but people who use the energy-capturing bikes say it encourages them to pedal harder and consume less. If you want to check out some off-the-grid workout equipment in New York City, head over to the Green Fitness Studio in Bushwick.