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Scientists have been astounded by the creation of a genetically modified "supermouse" with physical abilities comparable to the performance of the very best athletes - raising the prospect that the discovery may one day be used to transform people's capacities.

The mouse can run up to 6km at 20 metres per minute for five hours or more without stopping.

Scientists said that this was equivalent of a man cycling at speed up an Alpine mountain without a break. Although it eats up to 60 per cent more food than an ordinary mouse, the modified mouse does not put on weight.

It also lives longer and enjoys an active sex life well into old age, being capable of breeding at three times the normal maximum age.

American scientists who created the mice - they now have a breeding colony of 500 - said that they were stunned by the animals' abilities, especially given that the animals came about as a result of a standard modification to a single gene shared with humans.

They emphasised that the aim of the research was not to prepare the way to enhance the genes of people. However, they accepted that it may be possible to use the findings to develop new drugs or treatments that could one day be used to "enhance" the natural abilities of athletes.

The professor of biochemistry at Case Western Reserve University at Cleveland in Ohio, Richard Hanson, said the physical performance of the mighty mouse could be compared to supremely fit athletes such as the cyclist Lance Armstrong, who won the Tour de France seven consecutive times from 1999 to 2005.

The genetic alteration to a gene involved in glucose metabolism appears to stimulate the efficient use of body fat for energy production. At the same time, the mice do not suffer from a build up of lactic acid - which causes muscle cramps - a feature also seen in the best endurance athletes.

Professor Hanson said yesterday: "They are metabolically similar to Lance Armstrong biking up the Pyrenees. They utilise mainly fatty acids for energy and produce very little lactic acid. They are not eating or drinking and yet they can run for four or five hours. They are 10 times more active than ordinary mice in their home cage. They also live longer - up to three years - and are reproductively active for almost three years. In short, they are remarkable animals.

"On the downside, they eat twice as much as control mice, but they are half the weight, and are very aggressive. Why this is the case, we are not really sure."

He added: "We humans have exactly the same gene. But this is not something that you'd do to a human. It's completely wrong. We do not think that this mouse model is an appropriate model for human gene therapy. It is not possible to introduce genes into the skeletal muscles of humans and it would not be ethical to even try."

It may be possible for pharmaceutical companies to use the findings to develop new drugs that enhance muscle performance, which may benefit certain patients. Professor Hanson accepted it is possible athletes might misuse any future drug developed in this way.

- Independent