Some are attracted by speed, others by danger. Some crave competition, others need a hobby.
Celebrities ranging from actors to politicians long have been enticed by the sports world. The latest is a former champion athlete who remains a celebrity in retirement -- Lance Armstrong, who will run in next week's New York City Marathon.
A former triathlete whose remarkable endurance led him to a record seven straight Tour de France cycling titles, Armstrong is not among the contenders in the Nov. 5 marathon. Neither is supermodel Kim Alexis, who also plans to run next in New York.
Instead, they share a desire to conquer a new challenge, if not the world-class athletes. Armstrong is an exception, but even he's more focused on raising money for his cancer charity than winning the race.
The real contenders say they're glad to have celebs in the race.
"I think it's a definite help; it just gives us more publicity in the sport," said Deena Kastor, a strong candidate to become the first US woman to win in New York since 1977. "So it's fun any time you can relate to someone in the sport, search for their names in the listings."
Chef Bobby Flay, mountain climber Ed Viesturs, and former Olympic gymnastics gold medalist Shannon Miller are among the other celebrities signed up for the New York race. Flay completed the New York City Marathon in 2002. Viesturs and Miller will be running their maiden marathons.
Miller said she had considered running a marathon for several years, finally deciding she wanted to do it before turning 30 next spring. She ran a half-marathon in Jacksonville, Florida in early October to prepare.
"After I retired from competition, I was in need of goals. I always had a goal in gymnastics, whether it was the next meet or the next skill. Law school was one, and getting my undergraduate degree," she said. "I went sky diving. I learned to scuba dive. And I thought, `I should do a marathon.'"
European royalty such as Monaco's Prince Albert, a bobsledder, long have been involved in the Olympics. Actor Paul Newman became so fascinated with auto racing while portraying an Indianapolis 500 driver in the 1968 movie "Winning" that he went on to a successful racing career as a driver and team owner.
Performers ranging from Oprah Winfrey (1994 Marine Corps Marathon) to hip-hop entrepreneur Sean "P. Diddy" Combs (2003 New York City Marathon) to country singer Jo Dee Messina (2006 Boston Marathon) have tried their luck at the 42km distance. All finished, by the way.
Celebs have turned up at plenty of other sports events:
* Actress Geena Davis tried out for the 2000 US Olympic archery team.
* Actor Mickey Rourke was a professional boxer in the early 1990s.
* Percy Miller, a rapper known as Master P, had tryouts with several NBA teams and played in the Continental Basketball Association.
* Country singer Garth Brooks spent spring training with the Mets, Padres and Royals.
But not all celebrity performances have been fun and games.
Actor Jason Priestley's race car crashed head-on into a wall at nearly 290kph during practice for an Infiniti Pro Series race at Kentucky Speedway in 2002, breaking his back and both feet and leading to operations for foot, eye, nose and back injuries.
And US President Jimmy Carter nearly collapsed during a 10km road race at Camp David in 1979.