Andover's Caroline Kavanagh remembers well when she first got hooked on triathlons.

It was, after all, the first time she entered the three-sport (swimming, running, biking) competition, back in July of 2006 when her sister, Suzanne, unexpectedly entered her in a triathlon in Webster.

"I was really out of shape — I could barely run a mile — and it was a good motivator," said the 46-year-old Kavanagh, who played field hockey at Westford Academy and UMass Amherst. "But I wasn't expecting anything.

"I had never been a biker, runner or swimmer, but I actually did pretty well. It was a little painful, but I was thrilled and I caught the bug."

Yet, Kavanagh didn't progress to her current status as one of the more successful triathletes in the region, winning age-group honors on a regular basis, until last year when she joined TriFury, a local triathlon club founded in the fall of 2002 as an affiliate of the Merrimack Valley Striders.

"I'm not a club-type of person, but I wanted to get better and several people told me it would really help me," said Kavanagh. "It turned out to be the best thing I ever did. Once I started workouts with Sharon (Johnson, the team's coach), she really stretched my rubber band and I got more into the workouts I need.

"She challenges me, but makes it fun. The workouts are fantastic. It's not like a military drill — you feel like you're in your teenage days."

TriFury, the largest triathlon club in New England, jumped from about 50 members in its first year to about 100 the next year, reached 200 two years later and now lists over 300 members.

The tremendous growth appears to be a reflection of both the increasing popularity of triathlons and TriFury's philosophy.

Explaining the growth of triathlons, which first sprouted on a small scale about 25 years ago, Johnson said: "There's a lot of interest in being fit and living a healthy lifestyle and there is nothing better for you than the multi-training you get in triathlon training. When you see the people at a triathlon, it's like you're looking at a fountain of youth.

"It also coincides with the growth in cycling, which has become more popular, and if you train properly, you won't get injured. A lot of our (TriFury) members are runners who have been injured."

The club's growth is not hard to explain, according to 49-year-old Dave Tyler, one of the founding members of the club.

"Triathlons are a growing market, but a lot of triathlon clubs are exclusive — there are qualifying standards or you have to know someone," said Tyler, formerly of North Andover. "We're inclusive. We're about having members of all levels and we like to introduce people to the sport. I'd say relatively few are in for the competition and more are in for fitness and well being."

Johnson, 51, of Plaistow, N.H., who has competed in well over 100 triathlons, including the 2005 World Championships in Portugal, is coaching an interesting potpourri.

"It's quite a mix," said Johnson, who coordinates three workouts (swimming, strength training and cycle workouts) per week. "We have first-timers, people who have been doing it for a year and some veterans who are more about competition."

Two TriFury members, Thor Kirleis of North Reading and Mark Danieli, have been selected by USA Triathlon to represent Team USA at the Long Course Triathlon World Championships, Aug. 30-31 in Holland.

Another TriFury member, North Andover's Tom Licciardello, competed at the world famous Hawaii Ironman last year, finishing the 2.4-mile swim, 112-mile bike ride and 26.2-mile run in about 131/2 hours. Andover's Ken Shiff will compete in it this year. But most members have no great wish to work up toward that grueling event.

TriFury members range in age from the teens though the late 60s and efforts are being made to broaden the age span. TriFury has gotten involved in a program with Lawrence Family Services in which youngsters in grades 5-8 are being introduced to proper fitness, healthy living and — ultimately — triathlons.

For its members, TriFury is sponsoring a mini-triathlon (400-yard swim, 9.5-mile bike ride, 2-mile run) series this summer in Tyngsboro, mainly for beginners, and it supplies information and coordinates transportation for triathlon competitions throughout New England.

About TriFury

What: Local triathlon club, formed as an affiliate of Merrimack Valley Striders

When founded: 2002

Current membership: Over 300 — the largest in New England

Club goal: To promote triathloning at all distances, from sprint to Ironman, and to foster good fitness

More information: Contact info@trifury.com

Standard triathlon race distances

Sprint: 1/2-mile swim, 12.4-mile bike, 5K run

Olympic: 0.93-mile swim, 24.8-mile bike, 10K run

Half-Ironman: 1.2-mile swim, 56-mile bike, 13.1-mile run

Ironman: 2.4-mile swim, 112-mile bike, 26.2-mile run