We all want to be in shape, but, as many who have broken New Year’s resolutions know, some of us just don’t have that natural get-up-and-go-to-the-gym. It’s why we use gamified fitness apps and gadgets, require incentives and coercion, and latch onto fitness fads that we think might have the answer.
The reason, it turns out, may be genetic.
In a recent study, researchers at the University of Missouri bred lines of “super runner” and “couch potato” rats based on the animals’ inclinations to run voluntarily on their exercise wheels. The rats who exercised most when left to their own devices were bred with each other over 10 generations into a line of—you guessed it—gym rats. Those that showed the lowest inclination to exercise were bred into a line of slothful rodents who couldn’t even be bothered to walk to the mailbox, for Pete’s sake!
But seriously, by generation ten, the super runners ran on their wheels 10 times more than the couch potatoes. They also ran faster and longer than their lazy counterparts.
The scientists then tested the rats for several physiological and cellular factors associated with exercise and sequenced each animal’s genome.
“While we found minor differences in the body composition and levels of mitochondria in muscle cells of the rats, the most important thing we identified were the genetic differences between the two lines of rats,” said co-author Michael Roberts in a press release. “Out of more than 17,000 different genes in one part of the brain, we identified 36 genes that may play a role in predisposition to physical activity motivation.”
Lead author Frank Booth put it more bluntly: “We have shown that it is possible to be genetically predisposed to being lazy.”