These are not the first genetically modified, high-endurance mice, but these new mice require no extra food to run longer and
further farther. The study tweaked the gene that controls the body's burning of fatty acids. Earlier experiments on mice focused on the consumption of glucose, the fuel for sprinting and explosive muscle power. The slightly larger muscles on these new mice were able to perform better without extra food. By burning body fat for better muscle performance, instead of glucose, the new mice did not require the higher glucose supply that the earlier high-endurance mice needed.