Ian Fung, whose weight ballooned after an unhappy transition to a new high school, now regularly works out at the Reston YMCA. (Evy Mages/FOR THE WASHINGTON POST)

You’ve bribed and threatened, cautioned and cajoled, and still your child wants nothing to do with physical activity. He just doesn’t enjoy riding a bike, hitting a baseball or taking a swim. She wants nothing more than to text her friends and sit in front of the Xbox.

Now what once was a nagging childhood problem threatens to become a full-blown health issue as adolescence arrives, weight issues begin and your child settles into sedentary patterns that can last a lifetime.

A few people I know have turned to a decidedly adult, if unusual, solution: hiring personal trainers for their teenage children.

It’s not for every kid. There are a number of factors you should assess before committing to this approach. And obviously it’s much more expensive than the local rec league or simply joining your son or daughter on an evening walk.

But before you dismiss the idea as a luxury for people with too much disposable income, consider Ian Fung of Great Falls, who, at 15, was making an unhappy transition to a new high school after moving from the Atlanta area. His weight ballooned to 290 pounds, and he was doing no exercise whatsoever.

“He was overweight, and he wasn’t happy,” says his mother, Linda Fung. “And something had to be done.”

She took him to the Reston YMCA to work out alongside her and tried training him herself. “That was a disaster,” Linda says. Ian saw her every attempt to demonstrate proper form as controlling. Finally, Linda signed him up for personal training, and by chance Ian was paired with one of the Y’s trainers, a charismatic 26-year-old instructor named Charles Jenkins.

Their relationship didn’t start smoothly. For months, Ian stubbornly resisted Jenkins’s efforts. Linda “had to basically drag him here,” Jenkins recalls.

“I wasn’t good at it,” Ian says. “And it was tiring. Really tiring.”

Today Ian, who will turn 18 in July, weighs 215 pounds. He works out with Jenkins three times a week and is taking a weightlifting class at school. He is into mixed martial arts, motivated, in part, by one of the sport’s champions, B.J. Penn.

“He’s the only famous half-Asian, half-white person I know,” Ian says.

It takes only a few minutes with Jenkins and Ian to see why one-on-one training has worked so well for the teenager. Jenkins is as much Ian’s friend and mentor as he is his instructor. The easy camaraderie between the two is obvious. That’s tough to build on a team where a single coach is responsible for 20 kids.

Individual training provides an “emotional safety net,” says Fabio Comana, an exercise physiologist for the American Council on Exercise, a nonprofit organization that, among other activities, certifies physical trainers. “Physical training is free of ridicule. Physical training is free of peer review.”

Failure at sports and damaged confidence are just two of the many possible reasons some kids lose their inborn love of movement, experts say. Video games and computers don’t help. Perhaps the demands of practice schedules on structured school and rec teams aren’t for your child. Some kids work after school. Working parents sometimes aren’t available to transport their children to activities. In some neighborhoods, it just isn’t safe to play in the park.

One-on-one training typically provides more flexible time frames at safe, accessible facilities such as YMCAs or in the home. For-profit gyms, seeing a new revenue source, have begun to provide programming for younger people, Comana says.

Still, there are a number of things to consider before heading down this road, experts say; chief among them are safety and cost. Comana recommends checking whether an instructor is certified by one of nearly a dozen agencies that accredit physical trainers, and determining whether a trainer specializes in youth programming. It’s worth taking the time to consult with parents who previously have hired your child’s trainer.

Various organizations, including the American Academy of Pediatrics, suggest age-appropriate exercise regimens. Check those carefully, paying particular attention to guidelines for strengthening exercises, Comana says. Kids often want to lift more weight than they should.

Ian Fung's training costs $540 for 12 sessions, money his mother considers well spent. But small group classes may provide nearly as much value at a lower price, says Comana, and activities that involve the whole family cost much less while setting a good example for children, says Brian Robinson, chairman of the National Athletic Trainers’ Association Secondary School Committee.

“I’m all for anything that will get kids moving,” says Robinson, whose organization provides on-field and in-school care for injured athletes. “You really can’t browbeat kids into exercising. That’s where they need a role model.”

“Do what you have to do,” adds Linda Fung. “Just keep trying.”

Q&A: Fabio Comana, an exercise physiologist at the American Council on Exercise, answered your questions about exercise and personal trainers for teens.

Twitter: Follow @postmisifts