Could a marathon ever be run in under two hours?

As thousands prepare for the London Marathon, the very best among them face perhaps the most awe-inspiring barrier in sporting endeavour - the sub two-hour marathon. But can anyone break it, asks Chris Dennis.

A marathon of 26.2 miles (42.2km) in 120 minutes - the very thought takes my breath away.

Expert opinion on whether it is possible is intriguingly divided.

For some it is the next great sporting barrier to be broken, for others it will always remain beyond the limit of endurance. Could it happen at the 2012 Olympics?
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The current world record holder, Ethiopian Haile Gebrselassie, who ran the 2008 Berlin Marathon in 2:03:59, has no doubt it could be done, but not in the next few years, ruling out the next Games.

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