does size matter?

Yes it does, concludes three social scientists, but it's not what you think. In their article, "Does size really matter?: a reexamination of Sheldon's somatotypes and criminal behavior" the authors (Sean Maddan, Jeffrey T. Walker, J. Mitchell Miller) present their findings that persons entering prison (they examined 5,000 Arkansas inmates) were more likely to be athletically built (around 2/3 of the prison population) than either overweight or skinny. Their research confirms the connection between physically fit body types and violent criminal activity implied by William Sheldon's earlier work.

Of course a correlation does not imply a cause. But I understand the correlation. One of the reasons I go to the gym is that I enjoy the feeling of strength and power it gives me. For me strength and power is a spiritual gift leading to self-discipline, mental health, leadership and the ability to care for others, but I can see that for other people physical strength and power can lead to violence. I also know as a physically fit person I'm more comfortable in risky situations because I feel I can take care of myself. Thus my physical fitness exposes me to potentially violent situations other folks would avoid.

On the other hand I can think of at least two reasons that physical fitness would tend against violent behavior. One, physical exercise relieves negative emotions like depression or anger. I come away from the gym happier (less prone to destructive behavior) than when I went in. And exercise makes my body more attractive, my social standing increases and I'm led away from anti-social behavior.

You can purchase the article here.