Aggression positively correlated to muscle development in boys

Boys who show aggressive tendencies develop greater physical strength as teenagers than boys who are not aggressive, says a study.

There are a couple of possible mechanisms that could explain the findings.

For example, it is possible that muscular strength and anti-social traits are both mediated by changing hormone levels from childhood through adolescence.

Or it could be that aggressive boys engage in activities that facilitate greater development of strength.

"This work was motivated by a long standing controversy over the relationship between physical development and personality," said psychological scientist Joshua Isen from the University of Minnesota in the US.

The researchers examined data from two large samples of twins, collected as part of the Minnesota Twin Family Study.

The researchers particularly looked at the children's levels of aggression and their physical strength at ages 11, 14 and 17.

The data revealed an interesting trend. Boys who showed high levels of aggression and those who showed low levels of aggression were equally strong at age 11, but their strength seemed to diverge over time.

Specifically, more aggressive boys showed greater gains in physical strength during adolescence in comparison to their less aggressive peers.

As expected, the data showed no relationship between anti-social tendencies and development of physical strength among girls.

The findings were detailed in the journal Psychological Science.