London Marathon winner Paula Radcliffe has described her decision to answer a call of nature during the race as "an embarrassing necessity".
Radcliffe had to squat by the side of the road at the 22-mile mark after her stomach reacted to her pre-race meal.
"When I'm racing I'm totally focused on winning the race and running as fast as possible," she told the BBC.
"I was losing time because I was having stomach cramps and I thought 'I just need to go and I'll be fine'."
Radcliffe took control of the race after seven miles and went on to win her third London and fifth major international marathon title.
Her time of two hours 17 minutes 42 seconds was the third fastest ever, and a world record for a women's-only race.
But the world record holder's unscheduled stop briefly evoked memories of the Athens Olympics, when she dropped out of the race.
"This was just needing to go and once I had gone I was fine," said Radcliffe, who beat second-placed Romanian Constantina Tomescu-Dita by more than five minutes.
"I wasn't worried about it in terms of a repeat from Athens."
She added: "I want to apologise to the nation. I didn't really want to resort to that in front of hundreds of thousands of people.
"I started feeling it between 15 and 16 miles and probably carried on too long before stopping."
Radcliffe's next major target will be the World Athletics Championships in Helsinki in August.
But she has yet to decide whether to focus her efforts on the marathon or the 10,000m.
"I would like to win both, so there is a difficult decision there," she said.
"I'd like to win a world championship on the track and I would like to win a world championship marathon."
Meanwhile, the organisers of the five big city marathons are discussing the creation of a "grand slam" format.
The concept could involve paying a special bonus to any athlete who wins all of the London, New York City, Boston, Chicago and Berlin races.
"We see the benefit some of the major sports organisations have derived from being much more than single events," said New York City Marathon director Mary Wittenberg.