Boys who are aggressive in their childhood tend to develop greater physical strength as teenagers, revealed a study conducted by Association for Psychological Science. The study suggested a link between male upper-body strength and aggressive tendencies, but the mechanisms that account for the link are not well understood.
Psychological scientist Joshua Isen of the University of Minnesota, Minneapolis, said, "This work was motivated by a long-standing controversy over the relationship between physical development and personality and the physiques of boys and girls increasingly diverge during adolescence, leading to a profound sex difference in physical strength, and there's also an observable sex difference in personality traits like physical aggression and risk taking."
The researchers analyzed data from two large samples of twins collected as part of the Minnesota Twin Family Study. The twins began participating in the study at age of 11-years and researchers followed up with them every 3 years. Researchers were specifically interested in looking at the children's levels of aggression and their physical strength at ages 11, 14, and 17. Aggressive-antisocial tendencies were measured using a combination of teacher and self-report ratings. Strength was measured using hand-grip strength, which is highly correlated with other measures of muscular strength and to gauge hand-grip strength, the children were instructed to squeeze a dynamometer as hard as they could in both their hands.
The study findings revealed that 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. The more aggressive boys showed greater gains in physical strength during adolescence in comparison to their less aggressive peers.
Isen said, "The pubertal changes responsible for males' superior strength were likely shaped by inter-male competition for mates which would explain why competitive personality traits correlate with physical strength among males only."
The study appears in the journal Psychological Science.