Some of the Bay Area's most finely tuned athletes were strapped to "super treadmills," then attempted to boost their vertical leaps on "jumping sleds."

"Get low, get low, reach back," trainer Austin Latour urged one of the crouching, grimacing athletes as the girl trudged backward and uphill on a treadmill to isolate her quadriceps. "How are your quads feeling? They burnin'?"

"Oh, yeah."

These weren't Olympic hopefuls or professional athletes seeking an off-season edge. Most of the athletes at Bodymax, a Pleasanton sports-training center, were too young to drive themselves home -- including 15-year-old soccer player Hillary Lind of Lodi (San Joaquin County), the one tangling with the treadmill.

The center and others like it in the Bay Area are visible signs of a $4 billion-a-year industry that is increasingly competitive and controversial.

Geared to kids as young as 8 years old, the centers bring advanced techniques once reserved for pros to young people -- from the varsity quarterback to the 11-year-old kid keen on making the traveling soccer squad -- with fees often totaling hundreds of dollars a year per athlete. Some centers have staff dietitians and consult with sports psychologists.

Young athletes say they enjoy the training and notice the results. Those who run the centers say their expertise teaches kids how to exercise properly and avoid injury while building confidence, work ethic and sportsmanship in a competitive culture.

But some youth sports experts say the trend is mostly a reflection of competitive parents and profit-seeking businesses. Critics wonder whether children should spend more time on the sandlot or exploring other interests.

The centers typically do a brisk business in pro and college athletes, but children are becoming their bread-and-butter. In addition to Pleasanton, centers have opened in Livermore, Concord, Castro Valley and Menlo Park. Ex-Oakland Raider Rich Martini plans to open Velocity Sports Performance in Dublin and two more in the South Bay.

In Vallejo, former Cal football coach and quarterbacks guru Roger Theder and others are developing the biggest project yet, the Mare Island Sports Academy, to train pros and kids from all over the country. The plan includes four dormitories for camps and three football fields -- one with an all-weather bubble.

On the leading edge of the trend are affluent, family-oriented suburbs such as Pleasanton, a cradle of youth sports talent where top athletes who don't go to Bodymax or to a one-on-one skills coach -- or both -- are becoming the exception.

"It's hard for kids to compete nowadays unless they do this," said Hallie Grossman of Danville, whose 13-year-old son, Cooper, is trained at Bodymax. He also works with a baseball batting coach in San Ramon. "I have mixed feelings about it," she said, "but Cooper always wants to go to Bodymax. If we saw signs that he wasn't enjoying it, we would end it."

After finishing a set on the "Pro Multi-Hip" at Bodymax, the 4-foot-11, 85-pound Cooper said through his dental retainer, "I just like baseball a lot. I'm a smaller person for my age, so it helps."

In a nearby weightlifting room, 15-year-old baseball player Kyle Adkins of Pleasanton said he plays on high school and club teams, trains at Bodymax six days a week and sees a pitching coach at a nearby facility called the Pitching Center.

"To play at the next level, you have to put in the work early," he said. "If you don't, someone else will, and they'll take your scholarship."

Kids at Bodymax and at the Riekes Center for Human Enhancement in Menlo Park, which also has super treadmills, said they were thrilled by the changes they saw in their bodies, by their strength and by their speed. Some talked about dreams of playing college or professional sports, while others had more modest goals: making a junior varsity squad or earning a starting position on a club team.

Will Taufoou, 17, of San Carlos, who hopes to earn a football scholarship, said he had worked out so hard at the Riekes center that he had vomited. The occurrence is often joked about, or treated like a badge of honor, at the centers. Center managers acknowledged that occasional vomiting is usually the result of athletes not eating properly before a session on the treadmill.

Amanda Haiman, a pediatrician at Lucile Packard Children's Hospital at Stanford, said vomiting can be a sign of heat exhaustion or heat stroke, and can cause severe dehydration or even cardiac arrest. "When you exercise to the point of vomiting, that's not good," she said. "It definitely should be taken seriously."

Bodymax training director Shawn Dassie said that kids set their own exercise goals, in consultation with parents, and that their health is monitored closely.

"We try to keep it light," said Dassie, who often has to turn away parents who try to enroll kids younger than the 8-year-old minimum. "If they enjoy being here and it's an outlet, that's good. If I can make them a better person, that's even more important."

Jay Coakley, a sociology professor at the University of Colorado who has written extensively about youth sports, said he worries that some young athletes are living in a "Disneyland-like development tunnel."

"Kids are taken to the entrance of this high-performance sports program, and it's beautiful. The rewards are all there. People are going to carry their bags and parents are going to adjust their schedules," Coakley said. "I want to know what happens over the next 10 years as they live in that tunnel, have opportunities foreclosed and bypass identities that could have been developed."

More than 70 percent of kids drop out of organized sports by the age of 13, according to the nonprofit National Alliance for Youth Sports. The National Collegiate Athletic Association says that in the past two decades, roughly 5 percent of high school boys who played basketball, football, baseball or soccer ended up playing NCAA sports, and 1 in 1,000 was drafted professionally.

Parents have never been under such intense pressure to ensure that their children stand out in sports, music and academics, Coakley said.

"The sports centers are a supervised and credentialed setting where they know their kids will be out of trouble and will be taught something," Coakley said. "It's hard for me to be very critical of parents. Sometimes they have part of their head in the wrong place, but for the most part their hearts are in the right place."

The training centers spring from a sports-centric culture that is particularly intense in the Bay Area's affluent suburbs, where parents have been known to take second jobs so they can pay for their kids to see trainers and play on traveling club teams that employ salaried coaches and trainers.

Some parents and coaches pressure kids to limit themselves to one sport at an early age -- to avoid losing the opportunity for a scholarship or to become a celebrity star such as golfer Michelle Wie or soccer prodigy Freddy Adu, who are both 14.

In the current girls high school soccer season, 18 of the Bay Area's best players have opted not to play for their teams in order to play club soccer exclusively. They say club soccer is more challenging and means better exposure to college scouts. The girls play for the Pleasanton Rage club, which is one of the most successful in the nation and has headquarters inside Bodymax.

The fever pitch of the sports culture translates into a healthy market for training centers. Started in 2002, Velocity, of Alpharetta, Ga., now has 14 locations nationwide and could open 50 more this year, said company spokeswoman Kira Perdue.

New outlets could drive prices down. A 90-minute session at Gamespeed of Concord is $30 to $45; teenagers at the Riekes Center pay $390 per quarter for three workouts a week; Bodymax charges $175 for two dozen 60- to 90-minute sessions over the course of six weeks, but most kids shell out $1,100 per year for unlimited use of the facility.

Bodymax, the Riekes Center and NovaCare physical therapy of Castro Valley buy equipment pioneered by exercise physiologist John Frappier of Fargo, N.D., who has sold 130 licenses worldwide. The treadmills are designed to mimic an old Soviet technique that had an athlete sprint while holding onto a car driving faster than the athlete's top speed, said Frappier, who studied the technique while on a 1986 trip to the Soviet Union. Bodymax last year added a hockey treadmill.

Gary Riekes believes the programs at the Riekes Center are an antidote to competitive culture. An idiosyncratic entrepreneur who once played football at Stanford, Riekes offers music, film editing and nature studies to go along with the athletics, and his nonprofit group offers scholarships and allows kids to work in exchange for club privileges.

Bodymax is intense and detail-oriented -- kids' performance results are tracked online in the Athlete Information Management System, where they can be compared with age-group results around the world. Riekes, by contrast, tries to foster a clubhouse atmosphere, with few mirrors and walls covered with pictures of kids and their artwork.

On a recent afternoon, a couple of kids cooked pasta in a central kitchen while an 18-year-old gave a drum lesson in a batting cage. Riekes talks about getting kids to "smile from the inside out."

Most kids were just there to improve their strength and agility, but Riekes said, "If kids think that's the only thing in life that makes them worthwhile, that's a problem."