Explainer: ACTN3

The ACTN3 gene comes in two variants and the test developed by the Australian biotech firm Genetic Technologies distinguishes between them. The test is based on research published by scientists at the University of Sydney and the Australian National University in Canberra. In a study published in the American Journal of Human Genetics in 2003, the researchers compared the versions of the ACTN3 gene present in 429 elite athletes from 14 different sports (50 of whom competed in the Olympic games) with 436 volunteers. The researchers found that elite performers were more likely to have particular combinations of the gene variants compared to the volunteer group.

Genetic Technologies claims this research allows it to distinguish between sprinters and endurance athletes with a simple mouth swab test. It says people with one version of the ACTN3 gene are predisposed to become sprinters, while those with the other are better suited to endurance events. Scientists in the UK have been sceptical about such interpretations. They argue that a single research study is not enough to prove that the ACTN3 test can meaningfully determine athletic ability - a series of studies would be required.

But researchers acknowledge the importance of genes in physical ability - they are thought to determine up to 40% of a person's potential. At the elite level, where even the smallest advantage can be the difference between winning and losing, the genetic factor is therefore critical. All else being equal, winning an Olympic gold medal would be near impossible without a close-to-perfect genetic contribution.