By Scott Malone

BOSTON (Reuters) - When she walks into Rio de Janeiro's velodrome in August as the best hope to lead the U.S. women's track cycling team to its first Olympic gold medal, Sarah Hammer will be acutely aware she might easily never have seen that moment.

The 32-year-old Californian found her sport early -- she received her first racing bike for her ninth birthday -- but by the age of 20 was burned out, and decided in 2003 to retire from racing after just two years competing at the elite level.

The next summer, while watching the Athens Games on television at her apartment in Colorado Springs, she came to deeply regret that decision.

"I was thinking, 'Oh wow, this is what I missed. I love track racing and this is what I missed ... I just kind of threw it away'," she recalled thinking as she watched New Zealand's Sarah Ulmer claim the gold medal in the women's 3,000 meters individual pursuit in world-record time.

"At that point in time, I decided to come back and do it, do it right, that I was going to do it differently," said Hammer, who has held that very world record since 2010.

For Hammer, who began racing neighborhood friends on BMX bikes long before her father, Cliff, bought her that first Peugeot 10-speed, and went on to win her first junior national championship in 1995 at the age of 12, that meant leaving road cycling behind her.

"For many years, people said I was doing it wrong," Hammer said in a phone interview during a break from training earlier this year. "Now we are all specialists. People still obviously do road racing, but you do it for the track."

'LONDON BOOST'

Hammer's results have proven her right: The two-time Olympian snagged two silver medals at the 2012 London Games, in team pursuit and the women's Omnium.

Then last March she led the U.S. squad to its first gold medal in women's team pursuit at the world track cycling championships in London.

"London was a huge boost for us," Hammer said. "It showed us that everything we're doing is right on track."

Hammer will be racing at Rio's Olympic Games with the same five-member team that bested Canada in London, riding alongside Kelly Catlin, Chloe Dygert, Jennifer Valente and Ruth Winder. Hammer will be the only returning Olympian on the pursuit team.

The team is up against stiff competition, with Hammer reckoning that the British, Canadian, Australian and New Zealand teams are all threats for podium spots. Once the team event is done, Hammer plans to race the multi-event Omnium as well.

"The big goal is that team pursuit medal," Hammer said. "I'd love to get another medal in the individual as well."

The knowledge that she could have missed any chance at Olympic glory, let alone three trips to the Games, keeps Hammer going through the hardest phases of training and racing, she said. There are many days like that for an athlete who is more than a decade older than her team mates.

"Now the name of the game is really recovery for me," Hammer said.

"I have one teenage team mate and others that are in their early 20s. In training, we do everything together, and then they say goodbye and get on with the rest of their days and I have another hour of work so that I can show up the next day ready to train."

(Editing by Rex Gowar)