Always finding excuses to skip the gym? Congrats—you might be able to blame your genes. Because the mere desire to exercise may be inherited, at least in mice. So says a study in the journal Proceedings of the Royal Society B. [Theodore Garland Jr. et al., http://bit.ly/crWNGd]

The experiment started back in 1993 with 224 mice, divided into eight groups. In four of the groups, the researchers mated the males and females that logged the most distance on their exercise wheels. For the other four groups, they just randomly bred the mice.

Forty-three generations later, the mice descended from long distance runners are voluntarily running seven miles a day—three times as far as their lazy counterparts. And they cover those miles in different ways—some are marathoners, while others, especially females, run faster for fewer hours.

The running mice do have physical advantages, like better endurance and less body fat. But it's not just fitness. Previous studies suggest something's changing in the mice's brains, too, turning them into exercise addicts. And since mice and humans have similar genes, our itch to hit the track might also depend on how often mom and dad liked to throw on their running shoes.

—Christopher Intagliata

[The above text is an exact transcript of this podcast.]