Previous studies done on exercise habits among fraternal and identical twins have suggested that the propensity for exercise was a heritable trait, although not much more has been uncovered since then. But, a new study conducted by researchers at the University of Missouri may have figured out just how your genes determine your relationship with exercise.
The scientists selectively bred two groups of rats based on how much they ran (voluntarily) on an exercise wheel, ending up with one group of avid rat exercisers and one group of exercise-averse rats. They then studied the brains of young rats from both groups. As it turns out, the rats that were bred to enjoy exercise had higher numbers of mature neurons in the nucleus accumbens, the part of the brain associated with reward (for example, the so-called "runner's high" of post-workout endorphins). Even before the rodents had set foot on the wheel for the first time, this increased function in the nucleus accumbens meant that the gym-bunny rats were more likely to enjoy exercise (and to a greater extent) than their couch-potato counterparts.
Still, all is not lost for those born without the gym-rat gene. When rats from the exercise-averse group were forced to work out, the study found they developed more functioning neurons in the nucleus accumbens. So, even if you may never truly love exercise, you might be able to train your brain to reap some of the same rewards as those who do. Maybe it's time to hit the gym? (The New York Times)