a man running on a pathIf you do not enjoy exercise, it might be partly due to your genetics. Researchers from the University of Missouri conducted a study using rats to observe the effects of genetics on willingness to exercise. They found that rats who were genetically predisposed against exercise had an impoverished neural network in the brain’s reward center, which could make them less interested in exercising. The implications of this study for humans are murky, but it may help explain why some people avoid exercise, even when they understand the benefits.

Building on other studies suggesting that genetics might be a significant factor in enjoying exercise, the researchers bred rats that demonstrated a propensity for or disinterest in exercise. They bred rats together that willingly exercised on the wheel with or that showed little interest in running. After multiple generations, the scientists had two distinct groups of rats: one that ran willingly and one that barely touched the exercise wheel.

The results indicate that there is a difference in the brain’s genetic activity between the two groups of rats. The brain has certain genes that create proteins which tell brain cells to find a niche. When these genes do not work correctly, the rest of the cells do not receive the chemical messages they need and thus do not join the neural network or contribute to the brain.

For the willingly exercising group of rats, these genes functioned normally, but the exercise-averse rats had a deficit in the nucleus accumbens, which plays a part in processing rewards. This part of the brain is active for humans—and other animals—when people engage in activities they enjoy. The researchers found that, by adolescence, the willingly exercising rats had more mature neurons in the nucleus accumbens than the exercise-averse rats, even when neither group had done much running. This indicates that the brain’s of the willingly exercising rats were primed to find running a rewarding pursuit.

In the last phase of the experiment, both groups of rats were put on running wheels. Although the exercise-averse group did not run as much, their brains changed. After six days of running, they had more mature neurons in the nucleus accumbens.

It is “impossible to know at this point” exactly what these findings mean for humans, the results may suggest “that humans may have genes for motivation to exercise and other genes for motivation to sit on the couch,” explained Dr. Frank Booth, professor of biomedical sciences at the University of Missouri, who lead the study.

The good news is that people can choose to exercise, regardless of their genetic inheritance and the brain will adapt.

This research is published In The Journal of Physiology.

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