HEAVY BURDEN; SOME TEENS DOING TOO MUCH, TOO SOON AT GYM.

Byline: Phil Davis Staff Writer

Nicholas Murillo's brow furrows in concentration, his biceps taut as he lifts weights at the Spectrum Club in Valencia.

In the bright gym around him, dozens of middle-age corporate executives are fighting the battle of the bulge on stair machines and exercise bikes. But a fortysomething pot belly is not a concern for Nicholas, at least not for another three decades or so.

The 13-year-old Valencia seventh-grader is more concerned about bulking up enough to impress the coaches who will pick the eighth-grade football squad at La Mesa Junior High School next fall.

Meet the next generation of fitness club denizens - fresh-faced youths who aren't waiting until they're eligible for a corporate discount to workout at fitness centers. But whether they are rushing things remains a question.

Across the room from Nicholas on a rainy Tuesday afternoon, Ashley Stephens, 14, of Saugus, works up a sweat on an exercise bike, building endurance for dance classes and hoping to ``get a little thinner.''

Eighteen-year-old soccer goalie Ashley Breakfield, a senior at Valencia High School, is starting her second year of intense training at Spectrum with a personal trainer - an effort she hopes will pay off with an invitation to Olympic training camp or, at least, a college soccer scholarship.

Daniel Worth, 14, of Valencia said he works out at Spectrum to get an edge on the baseball field.

``I'm trying to get an advantage,'' said Daniel, a shortstop on the Valencia Titans baseball team. ``We have a weight room at school, but this is a lot better.''

Teens are still a rarity in most health clubs, but Spectrum's Teen Fit program has been a hit - especially in suburban Valencia where 211 teens signed up. A teen membership costs $95 in initiation and amenities fees and $25 a month, compared to $240 and $58 a month for adults. Teens are only allowed in the gym during off-peak hours.

Spectrum's teen program and the trend of wealthy parents hiring personal trainers to work out with their children has sparked debate in the medical community. Critics say gym memberships force an adult fitness regimen on teens, depriving them of the sheer fun of athletics. There's also a concern that still-developing muscles and bones might be damaged by repetitive activities such as lifting weights.

Dr. John DiFiori, a professor of sports medicine at the University of California, Los Angeles, said that children are more likely to develop overuse injuries in structured training programs.

``There are two ways of looking at it,'' DiFiori said. ``If you roll a basketball down a driveway and let a kid shoot baskets, they're not very likely to have an overuse injury develop. If you put a child in a situation where they are being asked to achieve a certain level of intensity of activity and they're trying to reach that goal, that is a setting where overuse injuries can occur.''

Teens like Nicholas are just hitting their maximum growth spurt, which some research shows can make a body more susceptible to injury. Take gymnasts. DiFiori said there is compelling evidence that stress on the growth plates in young gymnasts' wrists may interfere with development of the wrist joint.

Spectrum trainers are told to keep an eye on teen members. They know the kids will try to push it - either because of unsupervised weight training at school or peer pressure to max out weights.

``They think if they can do two exercises, 10 is even better,'' said John Farr, a certified personal trainer. ``I tell them, `Less is more, less is more.' I teach them that they have to give themselves time to recover or they're just working against themselves.''

The trainers say they are careful not to push teen clients too hard.

``A lot of it depends on age,'' Farr said. ``The younger the person, the easier you have to go on them. Their joints are still growing. Their bodies are still growing. You cannot push them as hard as you can an adult. You could seriously damage someone, and that could be with them the rest of their lives.

''And, also, kids want to have fun. It's supposed to be fun.''

Still, in an increasingly sedentary age where kids are as likely to play baseball on Nintendo as they are in a sandlot, it's hard to knock regular exercise. DiFiori said teens could benefit from workouts in a well- maintained, closely supervised gym as long as the equipment can be adjusted to fit their smaller frames.

``If they enjoy going to a gym with their friends and riding the exercise bike and shooting some baskets or lifting weights in a supervised environment, that's just a new setting for kids to interact and be active,'' he said. ``That's great.''

The teens are glad to get access to top-notch equipment.

``It's a lot better than school,'' Nicholas said. ``I don't think I'd do it if I couldn't come here.''

CAPTION(S):

4 photos

Photo: (1 -- color -- cover) Generation flex - Teens heading to the gym might not gain from the pain.

(2) Dancer Ashley Stephens, 14, of Saugus, works out on an exercise bike at the popular Spectrum Club in Valencia.

(3) Certified personal trainer Larry Painter guides 18-year-old Ashley Breakfield on a therapy ball to improve her balance.

(4) Nicholas Murillo, 13, a seventh-grader at La Mesa Junior High, strains while working out in hopes of making the football team next fall.

Andy Holzman/Staff Photographer