Endurance athlete's genetic edge has long running history

A gene variation commonly found in endurance athletes most likely evolved as humans moved out of warm, food- rich environments to colder and harsher conditions, new research shows.

The common genetic variation - which separates endurance athletes from sprinters - is due to natural selection, according to Professor Kathryn North from the University of Sydney.

In a paper published in the latest issue of Nature Genetics, Professor Kathryn North and colleagues based at the Children's Hospital at Westmead show that the variant form of the gene ACTN3, commonly found in endurance athletes, is also associated with more efficient muscle metabolism.

Those findings, added to data from DNA tests of individuals around the world, have led authors to conclude that ACTN3, the original "sprinters" gene, has evolved over millions of years to equip humans to cope with changing and more hostile environments.

"We can now explainhow this common genetic variation influences athletic performance as well as why it has become so common in the general population. There is a fascinating link between factors that influence survival in ancient humans and the factors that contribute to athletic abilities in modern man," said Professor North.

The latest paper builds on Professor North's groundbreaking study, published in 2003, which specifically linked two variations of the ACTN3 gene to athletic performance. Her discovery was that variations of the gene provided an important guide to whether an elite athlete has ability to be a power sprinter or an endurance performer.

In its most common variation, which accounts for about 80% of the Australian population, ACTN3 encodes for a protein called alpha-actinin-3. This is the protein which is found only in fast-twitch muscle fibres and is responsible for the explosive bursts of power necessary for successful sprinters or track cyclists. Among elite power athletes the alpha-actinin-3 protein is nearly always present.

Those with the variant form of the gene, about 20 per cent of the population, do not make the alpha-actinin-3 protein. Among elite endurance athletes - marathon runners and rowers - the variant form of the gene is more common.

Professor North's latest research has focused on how the absence of the protein influences muscle function. The authors have also looked at why the genetic variation has occurred.

In answering the first question, researchers developed a strain of mice which was completely deficient in alpha-actinin-3. They found the muscle metabolism of the mice without the actinin protein was more efficient: the mice were able to run, on average, 33 per cent further before reaching exhaustion than mice with the normal ACTN3 gene.

To answer the question as to why the variation occurred they looked at DNA samples from 96 individuals from around the world.

"Most Africans have alpha-actinin-3, it's the normal ancestral state. But as you move into European and Asian populations there is a marked increase in the number of people without the protein. In some Asian populations that number reaches 40 per cent, or even higher in some isolated populations," she said.

She believes the switch to more efficient metabolism is likely to have occurred due to natural selection during the last Ice Age, when humans began moving out of the food-rich areas of Africa into colder, harsher environments.