To See How She Runs, Look at Her Fingers

LONDON, Sept. 28 -- There are so many ways to look at a woman, including the ratio of the length of her index and ring fingers. It's a way to spot a good female athlete, say British researchers.

The lower the ratio, the better the likelihood the woman will be good at sports, suggested rheumatologist Tim Spector, M.D., of King's College London, and colleagues in the online edition of the British Journal of Sports Medicine.

In their study of hand x-rays of 607 women, they found that the higher the level of sport prowess achieved by the women, the lower their index-to-ring finger ratio (2d:4d) was likely to be.

"It can be postulated that this ratio may predict potential sports ability," the investigators wrote. "Understanding the mechanisms underpinning this relationship may give important insights into musculoskeletal fitness, health and disease."

It's been known for more than 50 years that there are sex-based differences in finger-length ratios, and in various studies of varying quality the differences have been linked to everything from sexual orientation, cognitive ability, and autism, to the age of development of breast cancer or myocardial infarction.

"There is speculative evidence that this ratio may be established during early fetal life, and there is some evidence that associates the prenatal sex hormone environment with 2d:4d," Dr. Spector and colleagues wrote. "It also appears that the ratio is stable during life. In most reported studies, males tend to have a lower 2d:4d."

Previous studies have also suggested that finger length ratio is associated with sports prowess among men, but few have looked at the possible association between 2d:4d and athletic ability in women, the authors noted.

To rectify this, they looked at standardized radiographs taken of the hands of 607 women (mean age 54) who were part of a twins registry. They measured the lengths of the second and fourth fingers of each hand, from the proximal end of the proximal phalanx to the distal tip of the distal phalanx. The 2d:4d ratio was calculated by dividing the lengths of the second digit by the length of the fourth, and the results from each hand of the same woman were averaged.

The participants had been asked to rank their highest levels of achievement, from age 11 on, in 12 sports: swimming, cycling, running, gymnastics, tennis, badminton, squash, golf, skiing, soccer, cricket, and martial arts.

Those participants who said they participated in one of the sports were then asked to rank their highest competitive level from 1 to 5, in the following categories:

• Social participation only (1)
• School team (2)
• Club/university team (3)
• County level (4)
• National level (5).

The investigators found that 2d:4d for both hands was 0.927 (0.019) (range 0.864-0.979). In all, 79% of the participants took part in swimming, 61% in cycling, 40% in tennis, and 37% in running.

The overall highest age-adjusted level achieved in any sport was significantly negatively associated with mean 2d:4d (b = 24.93, P=0.01). In separate analyses, mean 2d:4d was also significantly negatively associated with running level (b = 26.81, P=0.034), but not with other individual sports. Some of the strongest negative associations were with soccer playing individuals (b = 27.66), but numbers were small (n = 12). Only cricket, martial arts, and gymnastics showed non-significant trends in the opposite direction.

"Using a precise radiographic phenotype we have provided evidence that low 2d:4d is related to increased running and sporting ability in women," the authors wrote. "We postulate that 2d:4d is a predictor of potential sports ability. Understanding the mechanisms underpinning this relationship would give important insights into musculoskeletal fitness, health and disease. Further work may determine whether this ratio can be used at a pre-competitive stage to predict future ability."

They noted that their study data could have been skewed by their method of measuring X-ray images rather than hand photocopies, as used in other studies, and by recall bias, because there was no independent verification of the level of sports achievement each participant reached.