Unlike most 7-year-olds, Giuliano Stroe spends much of his playtime in his family’s Ciuresti (Romania) gym, lifting weights and toning his muscle-ripped prepubescent body. In one workout video recently posted on his popular YouTube page—Stroe’s videos have been viewed 13 million times—Giuliano benchpresses twice his body weight, flexes his biceps, and then growls at the camera like a cherubic Hulk Hogan. The boy owns Guinness World Records for (1) the shortest amount of time to walk 10 meters on one’s hands with a medicine ball between one’s legs and (2) the number of “air push-ups”—which are like normal push-ups except much harder, since one’s feet aren’t allowed to touch the ground. Stroe completed 20 without breaking a sweat.

Iulian Stroe claims his son became obsessed with strength training as a 2-year-old, if not earlier. “He has been going to the gym with me ever since he was born,” Iulian told the Austrian Times online newspaper last year. The hard work is paying off; Iulian recently announced that Tokyo-based Fuji Television Network paid him €1,000 (roughly $1,400) for a 30-second clip of his son in action. He declined to speak to Bloomberg Businessweek because, he says, he only does TV interviews now.

It’s easy to find the humor in a seven-year-old kid with six-pack abs when it happens in a foreign country like Romania. But children like Giuliano Stroe are no longer just a European eccentricity. In 2011, prepubescents and teenagers trying to mold their bodies into miniature versions of Arnold Schwarzenegger has become as American a pastime as apple pie and baseball. It may sound like an exaggeration, but Jay “Big Red” Cholewa, a 29-year-old Strength and Conditioning Specialist from Windsor CT who has trained children as young as 10, says that many of underage kids have weight-lifting abilities that would rival many adults. At annual events like the Iron Boy powerlifting contest in Fallston, North Carolina, he says, you can witness an 88-pound 10-year-old deadlift 150 pounds and squat 125. At the 2009 games, he says, a 12-year-old named Joel Delgado, weighing just 105 pounds, “deadlifted 240 pounds. That is quite a feat!”

According to IBISWorld, a market-research firm based in Los Angeles, weight-training gyms and private health clubs have grown increasingly popular among the 6-to-17 age groups. “Youth memberships have become one of the fastest growth areas for the fitness club industry,” says senior analyst Taylor Hamilton. “And many clubs have began shifting their focus to this area.” Over the last five years, the coveted preadolescent and teen memberships have increased by 2.9% annually, almost doubling since 2005. And the big draw isn’t the treadmill but the barbells. Jeff Martin, the director of youth programming for CrossFit Brand X, a workout center in Ramona, California, claims that their business has doubled in the last three years, and the majority of their new clients are underage. “We have kids coming in to our gym now who are 2 and a half, three years old,” says Martin.

Brian K Maloney, the Director of Fitness and Education at the Visions Wellness Center in New York City, believes that one of the reasons his gym is attracting a younger crowd is simply because he allows it. “Unlike a lot of health clubs and private gyms, who won’t let you work out in the weight room unless you’re 16 or older, our insurance covers younger members,” he says. It’s a growing trend among enterprising fitness centers across the nation, Maloney says, targeting an age group that has been mostly ignored (at least in the United States). At the Visions Wellness Center, rates for a strength training session for a pre-adolescent begin at $70. “We cater to people who have the money,” Maloney says about his mostly Upper West Side clients.

It’s not just the health clubs and gyms that are making a tidy profit. Weightlifting contests for teenagers and younger have become commonplace in recent years. This summer alone, there’s been the USAPL Teen & Junior Nationals in St Louis, MS (June 10-12), the GNC Teen and Masters Nationals in Pittsburgh, PA (July 21 to 23), and the 2011 ABA Natural North America Bodybuilding, Fitness and Figure Championships (August 13th, 2011); all either devoted to teenage powerlifters or with specials categories for contestants as young as 12 (and sometimes younger). And there are no shortage of kids eager to take part. At the relatively small High School National Powerlifting Championships, held last March in Corpus Christi, TX, the average number of contestants competing each year — who range in age from 14 to 18 years old — is, according to Director Hector Munoz, “around 400 lifters.”

The competitions are rarely charitable events. At the upcoming Junior U.S.A. Natural Championship in October — hosted by the INBA (International Natural Bodybuilding Association) in Columbus, Indiana — there are numerous opportunities for contestants, who range in age from 6 to 17, to be separated from their (or their parents’) money. The entry fee is $60 per contestant, with an additional $5 for processing. And then there’s the mandatory $50-to-$70 drug testing fee, and a $25 late fee if the entry form isn’t submitted at least fourteen days prior to the competition date. If a contestant wants a DVD recording of their “special day,” that’s available for just $79. Oh, and parents footing the bill for all this still have to buy tickets to the big show, which can run up to $45 per seat for premium seating.

And that’s just for one contest. The expenses involved in being a prepubescent weight-lifter can be surprisingly steep. Cholewa, who is currently pursuing his PhD in exercise physiology at Springfield College in Windsor, Connecticut, claims that the investment doesn’t end with a gym membership — which, by Cholewa’s estimate, can run anywhere from $600 plus a year. “I’ve known bodybuilders who spend upwards of $1,500 a year on supplements,” he says. And then, should a child have ambitions towards competitive bodybuilding, there are the private coaches, he says, who “charge anywhere from $400 to $2,000 for contest preparation, and that may not include any face-to-face personal training.”

With that kind of investment, one would assume that the financial payoff for a successful prepubescent or teenage weightlifter would be huge. But that’s not usually the case. The cash prizes for most junior weightlifting contests are low or nonexistent. This year, the annual Reebok CrossFit Games — which includes several weight-lifting events and takes place in late July in Carson, California — will be offering a teen division for the first time. But while the prize for top adult male and female athletes are $250,000 each, there is no cash prize for the teen division. CrossFit’s Jeff Martin explains that the lack of a financial incentive is to “avoid any conflict with scholarship opportunities.” When asked to explain why a cash prize would interfere with a student’s scholarship prospects, he admitted “I’m not exactly sure.”

Even if it’s not about the money, most trainers (and parents) are well aware that expecting a child to become the next Steve Reeves is putting the cart ahead of the horse. Jeff Martin at CrossFit says that when he’s working with a particularly young student, he tries to be creative. “You can’t tell a three year old to do three sets of ten curls for the biceps,” he says. “You tell a three year old, ‘Hey, let’s go across the monkey bars. Let’s do forward rolls.” Depending on their age, he might even just lead them on elementary lifting exercises, like holding up their backpacks. “It’s sometimes just enough to teach them how to pick up things correctly,” he says. “Later on, when they’re lifting actual weights, they won’t hurt their back as much as the adults who waited.”

How young can a child begin a strength-training regime? Andrew Farnell, the founder and president of Better Body Expert LLC — a personal training company based in North Brunswick, New Jersey — says almost immediately. “Some children come out of the womb ready to do this,” insists Farnell, who says that between 20 to 25% of his clients are children. It all depends on their kinesthetic sense, which he describes as an “ability to have a mind connection with your muscles.” Some children are born with it, he says, and some can’t lift any amount of weight safely because they lack that kinesthetic sense. “All children develop at different rates,” he says. “It’s not totally unbelievable that there are seven year old kids like Giuliano Stroe who excel at this.”

Mike Burgener, the 65-year-old founder and owner of Mike’s Gym in Bonsall, California, is a big supporter of strength-training among young children. In fact, he introduced his four kids, both girls and boys, to pumping iron around the ages of 8 and 9. His daughter Sage, he says, discovered the joys of exercising with a PVC pipe at just two years old. As his kids got older, he became more involved, and even signed on as the personal coach for his son Casey Burgener, who competed in weightlifting at the 2008 Summer Olympics. Burgener admits that he was “too gung-ho and over-bearing” with Casey, often pushing him harder than he did with his adult students. But he still believes strength training is a good idea for kids, if only for the “feelings of strength and confidence it gives them,” even if it occasionally means being screamed at by their overbearing fathers.

Parents who are hesitant about sending their children to the gym to lift weights may have legitimate reasons to be cautious. In a study conducted in March by the Research Institute at Nationwide Children’s Hospital in Columbus, Ohio, among the 970,000 weight training-related injuries reported during the last two decades, the vast majority of them (47 percent) occurred in people between the ages of 13 and 24. Strength trainers 12 years of age or younger suffered from the highest number of lacerations and fractures, and were more likely have a piece of weight-training equipment drop or fall on them than those 13 or older. But Brian Maloney claims that most of these accidents can be avoided with proper adult supervision. Once they learn how to operate the equipment safely, he says, the danger becomes negligible. Maloney’s five year old son Aidan enjoys working out on the strength training machines at his father’s gym, and according to Maloney, “his movements are better coordinated than the adults.” Sometimes, he says, when an adult can’t figure out how to use the bench-press machine, he’ll call over his son to demonstrate.

Cholewa says that with proper monitoring, “bodybuilding is fine at any age.” His main concern isn’t the physical toil of a weight-lifting regime — the worst case scenario, he says, is that a coach might need to occasionally measure the gravity of their student’s urine “to test for hydration” — but drug abuse. Over the past five years, he says, the emails he’s received from young bodybuilders, either teenagers or younger, requesting information about bodybuilding supplements has increased substantially. “I would say about 80% of the emails are questions about supplements,” he says. “What will work fastest; will product XX do this this and this; what do you think about stacking product XX with XY and YY?”

There’s no conclusive evidence that young bodybuilders and strength trainers are abusing supplements or even steroids. But a brief perusal of user profiles on the popular website Bodybuilding.com — acquired in 2008 by Liberty Media Corporation for more than $100 million — turns up many comments that at least hint at the possibility that underage weight-lifters, if not abusing drugs, are at least in need of a therapist more than a coach. “Steroids are a blessing for bodybuilders who are willing to sacrifice their bodies to be big and lean,” writes Jay Horowitz, a 15 year old from New York. “For motivation before a set, I hit my head and slap my face and get angry,” a 17 year old Joe Hagy proudly proclaimed on the site, adding that he’s been a body-building enthusiast for the last two years. “DAMN IT FEELS GOOD, and I hit those weights harder than I have ever hit them before.”

Dr. Dahlia Keen, a clinical psychologist based in Beverly Hills, California, believes that while strength training and bodybuilding activities may not necessarily pose physical dangers for adolescents, there can be hidden emotional dangers. “It is never a good idea for children to be obsessed with physical perfection,” she says. While a healthy lifestyle that includes fitness can have positive effects, especially among adolescents, when it’s pushed too far and “little boys start to look like mini men, it can be brutal.” Childhood should be a time for fun and creative play, Dr. Keen says, and more age appropriate activities. “Body building,” she adds, “does not tickle.”

(This story originally appeared, in a slightly different form, in the July 15, 2011 issue of Bloomberg Businessweek.)