Serena toured a locally based shoe and clothing company Wednesday and received occasional outbreaks of applause from Zappos.com employees. Her walk-through provided a hint to the sisters' staying power: They have been and continue to be about more than just practicing and playing tennis, avoiding the burnout that prematurely ended so many other promising careers.

"We have different interests, whether it's fashion or whether it's starting our own companies or things like that," Serena said. "I think for the most part it was able to sustain us and (help us) have a longer career."

Tennis, of course, led to other ventures. As fun and interesting as stepping outside the sport can be, Serena won't wander off too far.

She is preparing for next month's Olympic Games in Beijing and will head into full-time training this weekend. Serena said her injured left knee won't be a problem, though she withdrew Tuesday from the East West Bank Classic in Carson, Calif.

"It was really just fatigue," she said. "I've been playing so much tennis for the past four or five months, and I haven't really had any time off. So it was just saying, 'Serena, take a break. Take a couple of days off and just relax.' "

The eight-time major champion said she is especially excited about competing in the Olympics. The sisters won the gold medal in doubles at the 2000 Games in Sydney, Australia.

"Of all the tournaments I've won, my gold medal is my absolute favorite, the only one where I'll be, 'Look what I have,' " Serena said. "So I just love that I have an opportunity to play again."

On July 5, the Williams sisters won the Wimbledon doubles title, improving to 7-0 in Grand Slam finals. The victory came just 31/2 hours after Venus defeated Serena 7-5, 6-4 for the singles championship.

Sure, it was her sister she lost to. And, sure, they went on to win the doubles title. But ...

"It doesn't make anything easier," Serena said.

Her resume is among the best in women's tennis history. She has won two Wimbledon and two U.S. Open singles titles to go with three Australian Opens and one French Open.

Serena won three majors in 2002 to claim the No. 1 ranking, and she has finished in the top 10 six other times. She is currently ranked fifth.

While former rivals such as Martina Hingis fade into retirement and others such as Lindsay Davenport try to recapture their old form, Serena remains a championship-caliber player with no plan to step aside.

"I don't see an end right now," said Serena, who turns 27 in September. "I'm having so much fun this year. I've been playing a lot, and I've been enjoying it."

Contact reporter Mark Anderson at manderson@reviewjournal.com or 702-387-2914.