In the research published in the American Journal of Physiology, Booth and fellow research Michael Roberts put rats in cages with running wheels and kept records of how much each rat willingly ran on their wheels over the course of six days.They then bred the 26 rats which ran the most with each other, and bred the 26 rats which ran the least with each other. They repeated this process through ten generations of rats and found that the rats which originally ran the most ended up choosing to run ten times more than the ‘lazy’ rats.The scientists then found differences in the muscle cells of the rats and their body composition.“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 Roberts.“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.”The scientists are planning to continue to research the effects each gene has on people’s motivation to exercise. In the meantime, you can tell yourself this when you’re questioning why you still haven’t done the washing.Explainer: Why we grunt at the gym > Read: Penis size does matter to women – researchers > LOOKING FOR AN excuse for why you spent three hours on the couch last night? Trying to figure out why you still haven’t gotten around to doing that thing your boss asked you to do?Researchers in the United States may have an answer. Scientists at the University of Missouri have found that laziness may be genetic – which means no matter how good your intentions, it may be in your DNA to be a lazybones.The scientists at the veterinary department of the university were able to selectively breed rats which were either extremely lazy or extremely active. They say that these rats show genetics could play a role in whether people are motivated to move around and exercise or not.Professor Frank Booth who carried out the research said it could help to identify people who may become obese in later life.“We have shown that it is possible to be genetically predisposed to being lazy,” he said, adding:It would be very useful to know if a person is genetically predisposed to having a lack of motivation to exercise because that could potentially make them more likely to grow obese.