The piggyback training technique was not producing the results Ally Moore of Medina had hoped to see. "It was hard running up the stairs," she said of her unorthodox exercise regimen, which involved carrying her older brother, Bobby, around the house on her back.

Ally had watched her mom compete in the Ironman, a grueling half-day triathlon race. Now, with the summer "tri" season approaching, the 7-year-old was hoping to jump-start her fitness for entry into the sport.

"We bike in the neighborhood," Ally said. "We run on trails."

Ally and Bobby have also joined a local triathlon club, SCS Multisport of Eden Prairie, which has a program tailored to kids serious about competing in triathlon's burgeoning youth scene.

A competitive event requiring participants to swim, bike and run, triathlons have long been an adults-only pastime, with racer demographics skewing toward age 30 and older. But a spike in interest has prompted clubs such as SCS to form training groups for the 17-and-under set. High-profile races now commonly have kid-distance categories for which the little ones can paddle, pedal and sprint on the same day as Mom or Dad.

Events such as the MiracleKids Triathlon, which has races this summer in Chanhassen and Minneapolis, are attracting buff grade-schoolers and teens by the hundreds.

"It's a generational thing," said Steve Kelley, an athlete development coordinator with USA Triathlon (USAT), a Colorado Springs organization that governs the sport. "Triathlon became popular in the mid-1980s, and now many of the original participants have kids old enough to compete."

USAT has more than 21,000 members age 19 and under -- triple the membership of two years back. In 2007, the organization sanctioned 275 youth-oriented triathlons nationwide. A search on a sports-event website like now lists dozens of kid triathlons for each month of the season.

Kelley said the youth trend blipped on his radar around 2001. It has grown steadily since, bolstered by the sport's debut in the Olympic Games and a rising buzz as triathlons expanded from niche pursuit to more mainstream appeal. "Triathlon is not so exotic anymore," Kelley said. "When subplots on TV shows like 'Grey's Anatomy' are about tri, you know it's getting attention."

Jumping jacks, practice runs

SCS Multisport started its kids' program, called Yellow Dots, in 2005. About 20 Twin Cities-area kids attend the sessions at the SCS facility in Eden Prairie, where running, cycling and swimming instruction take place in a converted factory off Flying Cloud Drive.

This year's Yellow Dots program began May 12, a cool Monday evening when a dozen kids came in to train after dinner. "All right, welcome!" shouted John Shelp, a 36-year-old pro triathlete. "I'm Coach John."

The group, gathered in a circle on gym mats, went around show-and-tell fashion with introductions. Ally and Bobby Moore, sitting together near Shelp, fiddled nervously with water bottles. One girl sat idly in a leg cast. "Kate got a stress fracture from running," Shelp explained. "She was running really, really well before that happened."

Training for the night took place outside in the parking lot, where Shelp and his assistants led calisthenics and running drills. Ally, decked out in a SpongeBob bike jersey and excited to get on the move, attempted to squelch a smile during jumping jacks. "OK, one, two, three, four. ... " Shelp yelled out.

Although distances for kid triathlons are shorter than in adult races, a tuned body is still necessary to compete. USAT-recommended course lengths for the youngest triathlon group include a 100-meter swim, a 2-kilometer bike ride, and a 1-kilometer run -- with no rest in between. The top bracket, ages 16 to 19, has competitors going 750 meters in the water, 20 kilometers on bikes and 5 kilometers on the run.

Races can be intense, as some are less than a half-hour long, with 100 or more kids splashing, pedaling and sprinting in a whirlwind of action. Winners stream ahead in close competition by just a second or two, scooting past the pack in a final physical burst.

Mental moves are key, too

Beyond muscle and sweat, SCS also exercises the Yellow Dots' brains, as the sport requires competitors to pace each section and maintain an overall race strategy. Kick too much while swimming, for example, and you kill your leg muscles for the rest of the race.

Making quick transitions is another skill. In a sport that requires athletes to slide out of wetsuits, change shoes and chug energy drinks to keep stamina stoked, wasted changing time can separate the winner from the oh-so-close second and third.

At the Yellow Dots practice, sitting on the sidelines, Kate Lowrey -- the girl in the cast -- described a nail-biter last August: "I got fifth place," said the 13-year-old from Chaska. "But first place was just a few steps ahead of me."

That race, the 2007 USAT Youth National Championships in Wisconsin Dells, Wis., drew young triathletes from 21 states. Quoted in a news release, a USAT official at the time said: "This is the future of the sport. You may see some potential Olympians racing on Saturday."

Indeed, that is Kate's goal. By age 17 she hopes to be wearing a Team USA jersey at the 2012 Olympic Games.

"There's a lot of work to do in the next couple years," she said, sitting in the grass, watching her fellow Yellow Dots train. "First, I've got to get out of this cast."

Stephen Regenold is a Twin Cities writer and author of the syndicated column