LOS ANGELES (AFP) - US swimmer Dara Torres turned back time at the Beijing Olympics - but not completely.

Torres, 42, became a hero for the over-40s as she won three silver medals in Beijing, but she said Wednesday that arthritis in her left knee has limited her training and has her headed for surgery - hopefully after an appearance in the world championships in Rome later this year.

"It's old age. I have arthritis," Torres said. "I basically have no cartilage left. After the summer is over, I'm going to have to get my knee fixed - I'll probably have to have major surgery."

In a conference call looking ahead to the US world championship trials next week, Torres said the knee had limited her training both in the water and out.

"Everything now is pretty much preventative," said Torres, adding that she might skip the 100m freestyle at the US championships because the turn is hard on the knee.

"It hurts some days to walk up and down the stairs," Torres said. "I need my everyday life back."

If she makes the world championship team, she will have surgery after the championships. Then she'll decide whether to keep competing.

"I really thought I was done in Beijing," she said. "I think I was quoted as saying 'Let the other kids have their day.'"

She got back in the pool just for exercise, "and after about a week of that I thought, 'To heck with it. I'll go for Rome.'"

Torres's own health hasn't been her only concern. Her coach, Michael Lohberg, was diagnosed with the rare blood disorder aplastic anemia last year and was back in hospital this week with a blood infection.

Torres said Lohberg had been able to coach her effectively in recent months, even if he didn't make it to the pool every day.

She said he was still planning to attend the US championships in Indianapolis.

"He said that he doesn't care what the doctors say. He's getting on a plane Sunday," Torres said.