It is not just girls these days who are consumed by an unattainable body image.

Take David Abusheikh. At age 15, he started lifting weights for two hours a day, six days a week. Now that he is a senior at Fort Hamilton High School in Brooklyn, he has been adding protein bars and shakes to his diet to put on muscle without gaining fat.

“I didn’t used to be into supplements,” said Mr. Abusheikh, 18, who plans on a career in engineering, “but I wanted something that would help me get bigger a little faster.”

Pediatricians are starting to sound alarm bells about boys who take unhealthy measures to try to achieve Charles Atlas bodies that only genetics can truly confer. Whether it is long hours in the gym, allowances blown on expensive supplements or even risky experiments with illegal steroids, the price American boys are willing to pay for the perfect body appears to be on the rise.

In a study to be published on Monday in the journal Pediatrics, more than 40 percent of boys in middle school and high school said they regularly exercised with the goal of increasing muscle mass. Thirty-eight percent said they used protein supplements, and nearly 6 percent said they had experimented with steroids.