Marathon swimming is so new that it's hard to obtain data on splits or compile any convincing evidence about strategy.

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Nyad's marathon swimming career began in July 1970, when she set the women's world record for the 10-mile swim across Lake Ontario: four hours and 22 minutes.

CNN: Nyad delays attempt to break distance-swim record

When it comes to marathon swimming, there's an even stronger argument for staying with the pack: It allows you to prevent others from drafting off you and preserve their strength at your expense.

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"There have always been two things that I have wanted to achieve - running a marathon and swimming the Channel, " said Patten, from Liskeard.

BBC: Patten aiming to swim the Channel

Gold in the men's open water 10-kilometer swimming marathon in the Serpentine, the lake in London's Hyde Park, went to Tunisian Oussama Mellouli.

CNN: August 10, 2012 -- Updated 2336 GMT (0736 HKT)

And experts predict that women could soon outperform men in long-distance swimming and the marathon.

ECONOMIST: A story as old as girl meets boy

The marathon, road cycling, triathlon, open water swimming and race walking are the events most at risk.

BBC: Rogge admits Beijing air concern

She learned that one of racers' biggest gripes is that it is too difficult to put on their shoes for the marathon run after they have just spent hours biking and swimming.

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At 42 years old, I competed in the Ultraman World Championships, a grueling three-day uber-endurance triathlon circumnavigating the Big Island of Hawaii that involves 6.2 miles of swimming, 260 miles of cycling and culminates with a 52.4-mile double marathon run.

CNN: From miserable man to 'Ultraman': A fitness journey