TOKYO — Olympic marathon gold medalist Naoko Takahashi is retiring.

"I'm fully satisfied with my career, and I have no regrets," the former world-record holder said at a news conference Tuesday.

Takahashi, 36, was the first Japanese woman to win a gold medal in an Olympic athletics event in Sydney in 2000. She won the Berlin Marathon in 2001 in 2 hours, 19 minutes, 46 seconds, setting a world record at the time.

But she has since been unable to live up to expectations due to a series of injuries. Takahashi failed to qualify for the Japan team at the Athens Olympics in 2004, and also missed the Beijing Olympics after finishing 27th in the Nagoya International Women's Marathon in March.

Takahashi, a national idol, had been in Boulder, Colo., for high-altitude training since May, but struggled to maintain fitness.

"I've reached the limit of my physical and mental strength as a runner," she said Tuesday.

"It's not like my leg hurts ... There is no specific incident that resulted in my decision," Takahashi said. "I just cannot stand in front of you as a professional runner anymore."

A tearful Takahashi said she was happy to have chosen running as a career.

"I still love running," she said. "I retire as a professional runner, but I want to keep running until I hit 50 or 60."