Any extreme sport, by definition, carries with it a serious risk of disaster.

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But what he does is closer to extreme sport than exploring.

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The search for more extreme sport will continue.

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You know those extreme sport hot-dog skiers?

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Zorbing - effectively throwing yourself down a slope in a giant ball - was invented in New Zealand in 2000 and is now a popular extreme adventure sport around the world.

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"I think we are becoming extreme in both directions, " says sport psychologist Dr Victor Thompson.

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So unlike a sport like football or hockey that can turn to rule changes to improve player safety, extreme sports are only going to become more dangerous as participants push the limits of what humans can do.

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In an extreme scenario, illness could force Olympics coaches to dig deeply into their player reserves for replacements, depending on each sport's rules, which are set by international governing boards.

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