He had cycled 80 miles from home in the pouring rain, pushing his body to its limits. After two months of intensive training while researching the gruelling regimes that Olympic cyclists endure, novelist Chris Cleave got off his bike, sat by the roadside and turned into a gibbering wreck.
"I just completely cracked. I didn't have the energy to turn my legs around anymore and I just found myself in tears. I just couldn't get my head together."
Eventually, shivering and wet, he phoned a taxi firm to take him and his bike home.
Cleave had taken on a hugely challenging cycling programme to research his latest novel, Gold, which focuses on two British female cyclists fighting for one place in the London Olympics.
Zoe is the ruthless, cunning competitor whose raison d'etre is to win, while Kate just wants to do her best for everyone else and has other issues, most significantly a nine-year-old daughter suffering from leukaemia, and a husband who once had a thing for Zoe.
Cleave's intensive training may have ended by the roadside on that rainy day but the aftermath continued.
"For about a month afterwards I was really ill. I'd over-trained and destroyed my immune system to the point where I didn't have the energy to fight things anymore," he said, adding that he had suffered two months of really bad flu and depression.
"It was like I'd flown close to the sun and had come crashing back to earth. I could hardly walk down the street. Six months later I went for a run in jeans and a T-shirt and was wheezing and coughing at the end of it."
It was a year before he sat on a bike again. At the time, he thought it was one of his most negative experiences but it gave him the idea of how he was going to write Gold.
"By that point I understood that athletes are more interesting than we give them credit for and their interior battles are psychologically fascinating.
"When I got sick, I understood the angle I had to take." Ironically, the 38-year-old author, whose previous novels Incendiary and The Other Hand were both bestsellers, says he wasn't particularly interested in the Olympics until he started to delve into the athletes' world away from the cameras. "If you were the 200th best footballer in the world, you'd be driving a Ferrari. If you're the 200th best cyclist you'd probably be working at a supermarket when you're not training.
"I chose cycling because it's so extreme. The demands of training are huge and the margins of victory are tiny. You can win or lose sprint cycling events by a 10,000th of a second."
He interviewed a number of female athletes including Rebecca Romero, the only British woman to win an Olympic medal in two different sports - a silver in Athens in 2004 for rowing and a gold in Beijing in the cycling individual pursuit in 2008.
"I wanted to find out what it was about her that means winning an Olympic silver was one of the worst rather than one of the best days of her life."
Cleave adopts the 'method acting' equivalent of writing, so followed a similar training regime to elite level cyclists for two months - 20 hours of training a week, sometimes up to 100-mile rides on hilly ground.
As he got into the second month, things went wrong. "I really started falling apart, not just physically but mentally. I just started to crack. It's incredibly difficult and painful. I found myself getting listless and uninterested in life, getting completely cut off and becoming utterly obsessed with the training, to the exclusion of everything else in my life. When the training was going well, I was really elated and when it was going badly I was really morose."
With a wife and three young children, it affected family life, even though they were used for his research for his previous novels. "I managed to convince myself that I was some kind of athletic hero and that even though I was a novelist I was going to become a pro cyclist. I totally deluded myself."
His wife, he says, was extremely supportive, understanding the extreme nature of his research.
The London Olympics may be an obvious peg for a novel, but Cleave has a knack of choosing topics of the moment.
His cycling has continued, but not at extreme levels. "After I'd managed to get a more humble idea of the kind of athlete I could be, I started to enjoy it a lot more. I'm a suburban dad, I'm not riding the Tour de France."
He'll be doing a 350-mile London to Paris ride over three days this month to raise money for Leukaemia and Lymphoma Research.
He was keen to raise money for the charity following the research he did into leukaemia, during which he shadowed consultants at Great Ormond Street Hospital in London. "I don't take one minute of mine or my family's health for granted anymore. It made me realise that any health and happiness you have is such a fragile state of grace."
The son of a brewer, Cleave was born in London but spent his early years in Cameroon, west Africa, when his father was relocated. It was fantastic, he recalled.
"We used to run around in the street with our phone numbers written on our chests in biro. Wherever you ended up at the end of the day, some responsible adult would ring your parents and they'd come and pick you up."
Returning to London when he was seven was a culture shock and he and his brother felt like outsiders for some time. "We moved to a grim house and went to a grim school. We just didn't fit in at all. It was hard to make friends."
He studied experimental psychology at Oxford before embarking on different jobs including becoming a teacher of marine navigation in Australia. On returning to England, he became an online journalist and then moved to lastminute.com, which is where he met his French wife.
He hopes to catch some of the Olympic events. "Before I wrote Gold I was really cynical about the Olympics.
"But the more I got under the skin of it, the more I realised that sport is a beautiful, dangerous and complicated thing. I ended up being hugely positive about it."