Playing football makes you shorter

Researchers report that repetitive blocking and tackling -- coupled with the weight of helmets and pads - can temporarily shave nearly half an inch off of players' heights.

They studied 10 high school football players -- lineman, defensive tackles, and others whose positions involved repetitive blocking and tackling. The average height of players before the game was 69.5 inches. Afterward, it was 69.2 inches.

Campbell says that it's well known that people shrink over the course of a day. "If you think of your body as an accordion, gravity squeezes you together as the day goes on," he says. Football, he says, accelerates the process in two ways.