Sibling Rivalry Isn’t New to These Athletes : Triathlon: Twins Joy and Joan Hansen used to race around the block as girls. Today, they’ll run, swim and bike against each other.

None of them had heard of triathlons and biathlons back then, but the Hansen youngsters used to stage neighborhood contests of their own, beginning in the front yard.

From the starting line in front of their home in Phoenix, John Hansen would send his twin sisters off, racing around the block in opposite directions, meeting back at the house, diving into the back-yard pool and continuing the race.

They are grown women now, 32 and living in different cities, but until Sunday’s Orange County Performing Arts Center Triathlon, Joan and Joy Hansen have never competed against each other in a triathlon.

“People will yell, ‘Go, Joan!’ or ‘Go, Joy!’ ” said Joy, of Newton Square, Pa. “We answer to both.”

Identical twins, they are remarkable athletes, notable for their nearly immediate success at almost every sport they have tried.

Joy, for example, qualified for the national collegiate cross country championships only three weeks after she took up running in 1976.

Joan, who lives in Seattle, was a 1984 Olympian in the 3,000 meters after she began running in college. She ran her first triathlon in July, after precisely three days of training. She not only won the amateur division but also broke the course record.

The Hansens were recruited together as college swimmers by the Arizona in 1976, but they left their marks on the record books as All-American runners after one of the track coaches spotted Joy on a campus jog and knew she was something special.

“I thought, one hour of running a day versus five hours of swimming? I switched,” Joy said.

Joan followed. But just as they had diverged as swimmers, with Joan gravitating toward the sprints and Joy specializing in distance events, they gradually took to different endeavors.

Before her college career was over, Joy grew intrigued with the modern pentathlon, a competition that includes fencing and shooting as well as swimming and running events. By 1983, two years after she finished college, she was a national champion.

Joan stayed active in track and was a six-time All-American in track and cross-country. In 1982, she set an indoor world record in the two-mile. In 1984, she made the Olympics, running in the 3,000-meter race made famous by Mary Decker Slaney’s collision with Zola Budd. In a much overlooked sidelight, Joan also fell but got up and finished eighth in a field of 12.

While Joan continued to compete in track, Joy took up triathlons in 1983, first as a hobby. But when she did well, she turned professional. With her national-class background in swimming and running, she needed only to improve on the cycling. In 1989, she was the U.S. Triathlon national champion. Last year, she made between $50,000 and $80,000, and won another of the sport’s major titles, finishing first in the Coca-Cola Grand Prix points race and beating Colleen Cannon, the four-time winner of the Orange County event.

Joan, after being disheartened by the latest in a series of calf injuries that set her track career back, decided to try it too.

“I’d been trying to get her into this sport,” Joy said.

The amateur competition proved no competition for Joan, who swept through a series of races and was named U.S. female amateur triathlete of the year.

“I was definitely thinking about the Olympics at that point last year,” Joan said. “But I was continually getting injured right before nationals. After five years of that intensity, it’s a release to find a sport where you don’t get injured as much.”

The longer, less-intense distances cause fewer injuries than short, concentrated races, Joan said. Although she doesn’t rule out returning to track to try to make the 1992 team, she is enjoying the change since starting to compete in the professional division.

Last year, although she and Joy would sometimes be at the same events, they competed in different divisions.

“I’d finish, and they’d take us off to the press tent, so I wouldn’t get to see her,” Joy said.

This time will be different, but it won’t be competition, Joan said. “We’re excited,” she said. “We love it.

“I’ve had so many questions about that. Some people say, ‘you must be looking forward to beating her.’ We don’t compete. People never understand. We share the same races. We don’t call them competition.”

Wary of the effects of a rivalry between siblings, and particularly identical twins, the Hansens’ parents programmed them to think of races in a different way long ago.

“The attitude they raised us with is to be the best we can, rather than to be the best we can related to someone else. That taught us to perform in athletics rather than compete,” Joan said.

But a race, after all, is a competition. Cannon, last year’s winner, is the top-seeded woman in the event, but the Hansens are tied for the second spot.

“If it’s a tight race, we’ll come across together,” Joy said.

That is exactly what they did at the national cross-country championships in 1979, when they ran for Arizona and finished 14th and 15th, less than a second apart.

“We did it unintentionally,” Joan said. “I didn’t know she was there, and she didn’t know I was there. We were just running, and it happened.”