Do you cringe when a friend tells you about the awesome burn she got at a spin class? Does the idea of a pre-dawn run give you nightmares? You may have been born that way.
A study in The Journal of Physiology claims that the motivation to exercise may be at least partially due to genetic factors. Researchers from the University of Missouri selectively bred two groups of rats: one group came from breeding rats that had run voluntarily on a wheel, while the other group contained the descendents of rats who preferred not to run.
Researchers examined the groups after several days of not running, and after several days of voluntary running, and found that mice with low voluntary running behavior had fewer mature neurons that are affected by running-induced dopamine plasticity — in other words, mice who don't want to run don't have as many neurons that benefit from one of the feel-good hormones released by exercise. The New York Times has a good explanation of this portion of the study: