A surprising number of Twin Cities teens and adolescents are trying to build muscle through exercise, diet and even steroids, according to University of Minnesota researchers, who worry that "buff" has simply replaced "thin" as the body type that kids idolize.

The researchers found that 90 percent of boys and 81 percent of girls exercised to improve muscle strength or tone -- while about 5 percent used steroids. The findings, based on surveys of 2,700 middle and high school students in Minneapolis and St. Paul, were published Monday in the medical journal Pediatrics.

Muscle building among athletes was no surprise, but the researchers found it's popular among non-athletes, too. Heavy kids were as eager as light kids to pump up. Middle schoolers were almost as interested as high schoolers.

Big muscles are simply more common among celebrities, sports heroes and even GI Joe dolls, said lead university author Marla Eisenberg, and that has influenced today's youth.

"We've got a lot of kids that have [muscularity] as a goal," she said, "which really speaks to some body image issues that might be analogous to some of the body image issues we've seen around being very thin -- more so for girls."

The use of steroids among young respondents disturbed researchers and some local medical experts. But they disagreed over whether the increase in muscle-building exercise is bad -- especially in a nation where youth inactivity and obesity have been dominant concerns.

Dr. Jamie Peters, a Fairview sports medicine specialist in Eden Prairie, said it's fine for adolescents to build strength through appropriate aerobic exercise and training -- saving heavier weightlifting until after puberty, when their bodies are equipped for rapid muscle growth.

"Between obesity and this, this looks pretty good," he said, though he warned that excessive exercise can lead to injuries and other problems.

Peters found it perplexing that one in three boys and one in five girls tried protein shakes or powders, though. Supplemental protein is generally pointless for kids who get enough protein in their regular diets, he said.

"They're just wasting a lot of money," he said.

Eisenberg said she worries that exercise and protein shakes would just be the start for middle school students, who might choose riskier strategies, including steroids, to maintain their physiques later on.

"If people are using relatively innocuous behaviors as middle schoolers," she said, "what might they be doing when they are 15 years old or 18 years old?"

Ethan Martin, 14, started strength training at 1st Athlete in Edina a year ago to improve at hockey, but kept up the training even after a concussion knocked him out of hockey. He is now measurably faster and stronger, and it showed on the football field this fall. Ethan's 10-year-old brother certainly noticed, and wanted to start training as well, but his father wouldn't let him.

"I usually make bad decisions when it comes to my kids and push them into [sports]," said Ethan's father, Brett, of Shakopee. "But just listening to the instructors, if you have them start lifting weight before their body reaches that maturity level, it could be bad for their joints and bad for their bones and muscles."

Girls and boys

The U has been studying youth and family eating and fitness behavior for two decades through its Project EAT surveys of local public school students. A review of the original surveys suggested the questions were skewed toward females and their behaviors, so researchers added questions on diet and exercise to build muscle, with males in mind, when they surveyed a new group of students in 2009 and 2010. Researchers were surprised to find strong interest regardless of gender.

The university paper found more interest in muscle-building activities than other studies on the subject had found. The researchers wondered if the results were skewed by a body-building craze at just one or two schools, but found widespread interest at all 20 schools in the survey.

At Edina's community center and high school facilities, girls are still the minority, but are gradually making up a larger share of the 210 to 230 kids who register for summer weight training.

Adequate supervision and guidance are key, especially for middle school students who might have misconceptions about strength training, said Josh Bettes, supervisor of the Edina community center weight room.

"They tend to hop on the bench right away and try to do a bench press," he said, when they should be pursuing resistance training and other exercises instead of heavy free weights.

While the broad interest in muscle building was the biggest finding of the new study, some demographic groups stood out. Asians showed particular interest. Given the survey's sample in the Twin Cities, this demographic group skewed toward Hmong youth.

Most troubling was the fact that Asian boys and girls were three times more likely to try steroids.

Training centers booming

Interest in muscle training is reflected in the rapid growth of youth training centers such as 1st Athlete and the ETS gym in Woodbury, which opened in 2010 and has since moved to a facility three times larger.

"We've definitely been very busy over the past year," said Sam Ward, ETS' head performance specialist, with almost all of the clients seeking improvement in athletics. He hasn't encountered teens just looking for bigger bodies.

Brett Martin says his son has a healthy perspective on his strength training. Sure, he said, he'd probably admit to liking a more muscular physique, but that isn't the goal.

"He doesn't have pictures in his room of bodybuilders, and it's not something he ever talks about," he said.

"He just talks about how he enjoys lifting the weights. I don't think he's doing it for an image thing at all."

Jeremy Olson • 612-673-7744