Aggressive boys, it turns out, develop into stronger teens compared to their weaker counterparts, a new study says.

Previous research has suggested there was a link between male upper-body strength and aggressive tendencies, but until now the underlying mechanisms remained a mystery.

"Our study is unique because we used a prospective longitudinal design to examine whether male-typical behavioral tendencies are related to pubertal change in physical strength," psychological scientist Joshua Isen, from the University of Minnesota, Minneapolis, said in a news release.

The researchers examined data from two large samples of twins, age 11, collected as part of the Minnesota Twin Family Study. They paid close attention to aggressiveness and physical strength at ages 11, 14, and 17, relying on reports from teachers and the participants themselves. To measure physical strength, they tested hand-grip strength, which is highly correlated with other measures of muscular strength.

Interestingly, boys who were highly aggressive and those who showed low levels of aggression were equally strong at age 11, but as time passed the more aggressive boys became stronger and stronger.

Isen and his colleagues tested this association on girls, and found no such relationship between aggressive-antisocial tendencies and development of physical strength.

So what's the reasoning behind these stronger teens? Researchers suggest that it could be due to changing hormone levels from childhood through adolescence, or simply that more aggressive boys participate in activities that facilitate greater development of strength.

Regardless, the team believes that these findings have an evolutionary origin.

"The pubertal changes responsible for males' superior strength were likely shaped by inter-male competition for mates," Isen explained. "Our findings indicate that other aggression-related characteristics - including deceit, risk taking, and lack of empathy - predict future development of strength in males."

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