7 impressive outdoor gyms from around the world

You won't find air conditioning or piped-in music here, just a vigorous workout.

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Green Heart at Shaw Park, Hull, United Kingdom

The UK's first Eco Wellness Zone, opened in 2012, was also its first human-energy-powered outdoor gym. As participants burn calories on four energy-generating units (a hand bike, cross trainer, fitness bike and recumbent bike), a central battery is charged to light the area at night. Users also have the option to charge their own cell phones. Future plans include a system that will feed the energy directly into the national grid.

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