For an instant guide to how fast a woman can run, look at her hands.
Women whose ring fingers are longer than their index fingers are quicker on their feet, offering a simple way of predicting who will win a race.
The discovery could be a boon for parents wondering whether to spend large sums on coaching by providing an indication of their daughter's chances of turning into a sports star.
Unlike men, most women have ring fingers that are shorter or of the same length as their index fingers. Only a few have longer ring fingers.
The finding adds to evidence that the ratio between the two fingers - not the length itself but their length relative to each other - is associated with several personality traits including sexuality, fertility, intelligence, aggressiveness and musical ability.
The difference is believed to be linked to the level of the male hormone, testosterone, to which the foetus is exposed in the womb. Scientists have suggested that the higher the testosterone, the more masculine the resulting foetus is likely to be, with its associated traits of strength, fertility and mathematical ability.
While a longer ring finger is associated with some desirable traits, such as musical skill, a longer index finger is associated with others, such as intelligence.
Professor Tim Spector, of the Twin Research Unit at St Thomas' Hospital, London, who carried out the latest study, said he had been sceptical about the claims.
"I didn't believe this stuff - I thought it was rubbish. Most of the studies were based on small numbers and the findings could easily be spurious."
He decided to test the claims because he had access to a large database of twins, on whom he has been doing research for 20 years. He examined x-rays of the hands of 607 female twins aged 25 to 79 and compared the lengths of the their index and ring fingers.
The results, published in the British Journal of Sports Medicine, showed women with longer ring fingers were significantly better at most sports, especially those involving running, such as tennis and soccer.
Professor Spector said: "I was surprised to find something. The idea is that it is due to hormone levels [of testosterone] in the womb. The longer the ring finger the more butch and the less likely to be gay you are. But also the more likely you are to die of heart disease."
It was unclear why the length of the ring finger should serve as a marker for a certain genetic makeup.
"It is highly unlikely that having a long ring finger is only good. If it is a male trait, and women who have it are more like males, then it is likely to be something hormonal.
"I would postulate there is likely to be a downside too - such as people with longer ring fingers are likely to die sooner. If it conferred an evolutionary advantage, everyone would have them."