Extreme Marathons

Participants in this 5-day event, billed as the ultimate test of human endurance, compete in disciplines such as canoeing, cycling, glacier hiking and mountain trekking.
John McConnico / AP

Extreme Arctic Challenge, Ammassalik, Greenland
Participants in this 5-day event, billed as the ultimate test of human endurance, compete in disciplines such as canoeing, cycling, glacier hiking and mountain trekking.

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