LONDON (AP) -- Kristin Armstrong seemed to be retiring at the perfect time.
The Olympic time trial champion had just won another world championship. She had competed in every major race, and won her share of them. She was 36 years old and ready to start a family.
There was only one problem.
She wasn't ready to get off the bike.
So after giving birth to her son Lucas in 2010, the American resumed the long hours that made her one of the best cyclists of her generation. And despite a broken collarbone sustained earlier this year, she'll be defending her time trial gold at the London Games on Wednesday.
"A lot of people ask, 'Why did I need to come back?"' Armstrong said. "After winning a gold medal and retiring with a world championship medal, what more is there?
"I realized the reason I stopped the sport of cycling is to have a child. I wanted to start a family, and as I was getting older, I wasn't sure how long it would take," she said. "Luckily for us, Lucas came into our lives a little over a year later, after the world championships, and I realized that I really wanted to continue on my bike. It's what I love to do."
The women's race begins at Hampton Court Palace and covers 18 miles before finishing back at the 16th century court that was once a favorite of Henry VIII.
Reigning Tour de France champion Bradley Wiggins and the rest of the men's field will start once the women finish, covering a similar 27-mile course in Middlesex.
Armstrong will be pushed by one of the deepest fields ever to contest the time trial.
Judith Arndt of Germany is the reigning world champ, and the only rider who beat Armstrong at the Tour of Flanders. Olympic silver medalist Emma Pooley of Britain will be trying to build on the silver medal that teammate Elizabeth Armitstead won in Sunday's road race.
Then there's Linda Villumsen, the world silver medalist, who was born in Denmark and competed for her native country until 2009, when she gained citizenship in New Zealand.
"It's a different experience, but I'm proud to be here," the soft-spoken Villumsen said this week. "I'm proud to represent the country, and I hope I can do well.'
Another rider to watch is Clara Hughes, a former speedskating gold medalist.
The 39-year-old Canadian won time trial bronze at the 1996 Atlanta Games, but didn't truly focus on the bike for more than a decade. Only recently has she concentrated on cycling again, and while she missed the winning move in Sunday's road race, she was encouraged by her performance.
"I felt really good," Hughes said. "I climbed every section at the front, so going into the time trial I have a really good sensation. I am really excited for Wednesday."
All of them will have their eyes on Armstrong, though.
"Kristin wouldn't have come back if she didn't think she could do it," said teammate Amber Neben, who will also be competing. "When she stopped, she was the best, so she hasn't lost that."
After her second-place finish at Flanders, Armstrong won four of five stages and the overall at the Tour of the Gila. And at the Tour of California, she was the only woman to cover 18.5 miles in under 40 minutes, her time besting more than 50 riders in the men's field.
Everything was going perfectly - almost too perfectly.
At the Exergy Tour in May, racing before a hometown crowd in Boise, Idaho, Armstrong fell during the opening prologue and broke her collarbone. She had surgery almost immediately, and her doctors allowed her to resume riding after only a couple weeks.
"The doctor said, 'Well, if the Olympics were in a week, would you race?' And I said, 'Absolutely. No question."' Armstrong recalled. "And he said, 'Listen, I wouldn't stop you from riding outside in a week if it was the Olympic Games, so I have no reason to stop you from riding outside tomorrow. Just go out there, be careful, don't fall."'
It was good advice, and she had taken it to heart until this past weekend.
Armstrong was competing in a rain-drenched Olympic road race when her tires went sliding out and she crashed to the tarmac. She was scraped and bruised, but managed to remount and finish in the main pack without serious injury.
Good thing, too, because nothing was going to keep her off the starting line Wednesday.
"Once you win gold," Armstrong said, "you don't want anything less."