I have about 12 friends who`ve decided to run their first marathon or half-marathon this year. Meanwhile, the thought of jogging a quarter-mile makes me want to go into hiding for the rest of the day. For years, I`ve been told that exercise relieves stress. Not so for me. I feel better when I get what needs to be done accomplished, then eat a good meal with interesting people and curl up under the covers.

Turns out, they`re may be more than my convictions to back me up. A new study published in The Journal of Physiology found that the desire and motivation to exercise could be, at least in part, genetic. You heard them: It`s not just a matter of busy schedules or laziness.

Researchers bred mice over many generations in order to separate them into two distinct groups: those who happily spent hours on running wheels and those who, for the most part, avoided them. Brain activity in the more active rats showed they were primed to find running rewarding, even before they`d done much of it.

But, that doesn`t mean that an aversion to working out is your destiny. When non-runner rats were forced to start moving, their brains began to change, responding in ways that made exercise more rewarding.

And while some people, like rats, may be predisposed to enjoy physical activity, genes aren`t destiny. "People can decide to exercise, whatever their inheritance," said Frank Booth, a professor of biomedical sciences at the University of Missouri who oversaw the study.

BDST: 1255 HRS, APR-10, 2014