Image caption There are too many 'macho' images, the researchers say

Modern-day superheroes promote a macho, violent stereotype for young boys, according to a US psychologist's study.

They differ greatly from superheroes of yesterday, who had a more vulnerable side, an American Psychological Association meeting was told.

The only alternative male role model in modern media was the "slacker" who shirked responsibility, the study said.

Professor Sharon Lamb surveyed 674 boys aged four to 18 to find out what they read and watched on TV and in films.

Today's superhero is too much like an action hero who participates in non-stop violence; he's aggressive, sarcastic and rarely speaks to the virtue of doing good for humanity Professor Sharon Lamb, Study leader

With her team at the University of Massachusetts, she then analysed the types of male role models the boys were exposed to.

It showed two main types of man - the aggressive superhero or the slacker who does not even try.

"There is a big difference in the movie superhero of today and the comic book superhero of yesterday," said Professor Lamb.

"Today's superhero is too much like an action hero who participates in non-stop violence; he's aggressive, sarcastic and rarely speaks to the virtue of doing good for humanity.

"When not in superhero costume, these men exploit women, flaunt bling and convey their manhood with high-powered guns."

Boys could look up to and learn from comic book heroes of the past because outside of their costumes, they were "real people with real problems and many vulnerabilities".

She said the other option for boys was to be a slacker.

"Slackers are funny, but slackers are not what boys should strive to be; slackers don't like school and they shirk responsibility.

"We wonder if the messages boys get about saving face through glorified slacking could be affecting their performance in school."

In a second presentation, Dr Carlos Santos, from Arizona State University, examined 426 middle school boys' ability to resist being emotionally stoic, autonomous and physically tough - stereotyped images of masculinity.

He found that being able to resist macho images - especially aggression and autonomy - declines as boys transition into adolescence and this decline puts their mental health at risk.

"Helping boys resist these behaviours early on seems to be a critical step toward improving their health and the quality of their social relationships."