WATCH: Breaking2 a Documentary by National Geographic

After six months of scientifically advanced training, three of the world’s most elite distance runners set out to break the two-hour marathon barrier. ➡ Subscribe: http://bit.ly/NatGeoSubscribe

Video via National Geographic

YouTube https://www.youtube.com/channel/UCpVm7bg6pXKo1Pr6k5kxG9A

Read more from National Geographic http://www.nationalgeographic.com/

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