Researchers at Case Western Reserve University in Ohio have managed to breed some "mighty mice", capable of running at top (mouse) speed on a treadmill for up to six hours without stopping.
These impressive wee beasties have been genetically engineered to have unusually high levels of an enzyme called PEPCK-C in their muscles. This enzyme is normally involved in glucose metabolism, and helps our bodies to make energy from sources such as glycogen and fat.
The researchers found that the mice eat 60 percent more than usual, but remain fitter, trimmer and live and breed longer than their normal counterparts. The mice were also tested on treadmills, and the scientists found that the modified ones could run for nearly twice as long as unmodified mice.
Lead researcher Richard Hanson compared the metabolisms of the mighty mice to cycling ace Lance Armstrong biking up the Pyrenees. He points out that these mice use mainly fat, rather than sugar, for energy, and produce very little lactic acid compared to normal animals. It's the lactic acid build-up in muscles that causes pains and cramps after intensive exercise.
The mice were bred as part of an on-going research project aimed at understanding the role of the PEPCK-C enzyme in muscle and fat tissue, and according to the researchers, they could tell from the start that these mice were a bit special, and apparently they ran continuously in their cages from an early age. But as well as being more active and virile, they're also more aggressive.
The scientists found that these traits continued for at least two years - that's considered old age in mouse terms. Some of the female mice were even having babies at the ripe old age of 2 and a half years, which is very unusual - as most don't breed after they're about a year old.