Young men—whether they were looking for their battlefield gore fix or a chance to geek out over the historical inaccuracies of a sex scene between Themistokles and Artemisia—lined up for the opening of 300: Rise of an Empire on Friday. And though some parents may forbid their teens from seeing the R-rated film because of the blood and violence, they should probably be more concerned about the Greeks’ sweaty, washboard abs.

We’re all familiar with the pressures on girls and women to look thin, but discussions of body image often overlook men—a demographic increasingly at risk for unhealthy behaviors due to body insecurity. Men are feeling increased pressure to add muscle mass and gain weight, not lose it.

The average guy wants 15-27 more pounds of muscle and a three to four percent decrease in body fat. And a new study published in JAMA Pediatrics in January found that 18 percent of boys are very concerned about their weight and physique. Failure to attain these unrealistic body goals can lead to depression, high-risk behaviors (like drinking and drugs) and eating disorders. Though about 15 percent of boys concerned with their weight are worried about thinness, about half are concerned with gaining more muscle and an additional third are concerned with both muscle gain and thinness.

Many of these changes are thanks to media images—and the 300 movie series is leading the way in the promotion of unrealistic male body standards (buttressed by video games and clothing ads featuring scantily clad men).

When the original 300 film hit theaters in 2006, a grueling fitness program called the “300 workout” swept gyms across the U.S. as men hoping to get gladiator-like bodies signed on. The workout, which was developed to get the cast of the films in fighting shape, has a pretty basic concept: 300 reps of various exercises with no breaks. But it is so intense that the cast had to train six hours per day, five days per week for four months before they could even attempt the 300 workout, and only one actor, Andrew Pleavin, was able to actually complete it. In a Men’s Health interview, Gerard Butler admitted that he could not workout for a year after filming 300 because the program made him so physically exhausted.

And yet publications like Men’s Health touted intermediate and beginner versions of the 300 workout. Instructional YouTube videos of similar workouts abounded. Suddenly average guys were aiming for 300 bodies.

Why? The ripped male bodies that grace our movie screens have boys thinking they’re inadequate. Research has shown that 25 percent of men with a healthy weight think that they are underweight. And a recent TODAY/AOL Body Image survey found that men worry about their appearance more than they do about their health, family, relationships or professional success. Fifty-three percent of men said they felt insecure about their appearance at least once a week.

Parents, teachers and doctors often miss male weight disorders because the symptoms are not the same as with females, according to a recent Atlantic article. Most eating disorder assessment focuses on girls who starve themselves or induce vomiting in order to look thin. Boys are engaging in a different type of unhealthy behavior—working out obsessively, taking natural but unregulated substances like powders or shakes to bulk up and even using steroids. Such efforts can hurt young boys’ growth and, in the case of steroids, cause behavioral problems, rage and depression.

“Instead of wanting to something unhealthy to get smaller, they’re using unhealthy means to become larger,” Dr. Alison Filed, an associate professor of pediatrics at Boston Children’s Hospital and the lead author of the JAMA Pediatrics study tells The Atlantic.

Health professionals are slowly defining the line between health-conscious behavior and over-the-top behavior for boys and men. But it will likely be a while before public awareness catches up to the dangers posed by the overemphasis on impossible physical goals.

Write to Eliana Dockterman at eliana.dockterman@time.com.