'Marathon men' make better sexual partners, media cl...

"Marathon runners are the best in bed," is the spurious claim in Metro.

The headline is based on a study that only looked at long-distance runners’ finger ratios – said to be a marker for high testosterone levels – not reported partner sexual satisfaction (or as other sources report, high sperm counts and "reproductive fitness").

The study is based on the concept of what is known as 2D:4D ratio – a measurement of the ratio between the length of the index finger (second digit) and the ring finger (fourth digit).

Previous research suggests that men with a low 2D:4D ratio (when their ring finger is comparatively longer) may have been exposed to higher levels of testosterone in the womb, which is linked to the potential for reproductive success.

Researchers wanted to see if running prowess in males could be a sign of their evolutionary reproductive potential (as measured by their 2D:4D ratio).

They found that men with more "masculine" digit ratios – i.e. longer ring fingers – did better in the 2013 Robin Hood half marathon in Nottingham than those with the "least masculine" ratios. The same link was found in women, albeit to a lesser degree.

Researchers did not look at whether these more "masculine" men were judged to be more attractive by women.

Where did the story come from?

The study was carried out by researchers from the University of Cambridge and the Institute of Child Health, London. There was no external funding.

The study was published in the peer-reviewed medical journal PLOS ONE. This is an open-access journal, so the study is free to read online.

Reporting of this study by the UK media was almost universally poor, with many sources making claims that were not supported by the study:

Mail Online: "Those who run endurance races get more dates and have a higher sex drive" – unproven
Metro: "Marathon runners are the best in bed" – unproven
The Daily Telegraph: "Good runners are likely to have had ancestors who were excellent hunters… creating a biological advantage for their descendants and passing on the best genes" – unproven

At least the Daily Mirror and Huffington Post tempered their coverage with a "may" and a "probably".

None of the media coverage made it clear that the study was using running ability as a proxy for hunting prowess in pre-agricultural societies and had little or nothing to do with modern relationships.

What kind of research was this?

This was an observational study that aimed to test the researchers' theory that physical prowess at endurance running is associated with male reproductive fitness. In this study, the researchers used the digit ratio to predict reproductive success. This is the ratio between index and ring finger, which is a marker of hormone exposure in the womb.

The researchers explain that the high value placed by females on male ability to acquire resources has been well documented, especially in pre-industrial societies. Before agriculture developed, hunting ability may have provided an important way of demonstrating male resourcefulness and seems to be linked to fertility, offspring survivorship and number of mates.

There are several theories that try to explain this link; one is that hunting success is a reliable signal for underlying traits such as athleticism, intelligence or generosity in distributing meat.

In “Persistence Hunting” – one of the earliest forms of human hunting – prey often required running for long distances. This may act as a reliable signal of reproductive potential, say the researchers.

Since increased testosterone exposure in the womb is associated with reproductive success, an association between testosterone and endurance running would make running prowess a reliable signal of male reproductive potential, they argue.

What did the research involve?

The researchers recruited to their study 439 men and 103 women taking part in the Robin Hood half marathon in Nottingham in 2013. Participants ranged between the ages of 19 and 35, and were all white (Caucasian). The half marathon, they say, was chosen for its appropriateness to pre-agricultural, hunter-associated running and reflects endurance running ability.

All competitors wore small electronic chips to guarantee accurate race timings.

Photocopies were taken of the athlete’s left and right hands on finishing the race and these were used at a later date to measure the 2D:4D ratios.

The digit ratios were measured using special electronic callipers and were taken twice from each photocopy, to ensure accuracy.

The researchers then analysed the results, looking for an association between the digit ratio and the race time in each sex.

What were the basic results?

They found that among the men there was a "significant positive correlation" between right and left hand 2D:4D ratio and marathon time, with higher levels of performance associated with a lower, more "masculine", digit ratio. The correlation strengthened after controlling for age. The same was true of the female sample, but to a lesser degree.

How did the researchers interpret the results?

The researchers say their results support the theory that endurance running ability may signal reproductive potential in men through its association with prenatal exposure to testosterone. Running prowess they suggest, could act as a reliable signal for male reproductive potential.

Conclusion

This study of distance runners and their digit ratios, and the possible relationship between successful hunting and male reproductive potential, is a little tenuous.

This was an observational study using long-distance runners as a proxy for hunters and digit ratio as a proxy for reproductive potential. The most it can show is an association between the two.

It should also be noted that:

the study did not assess any non-runners
the runners' ability was measured in only one race
many qualities contribute to marathon running success, including muscle strength and mental endurance
the study only included Caucasians, so the results may not apply to people of other ethnicities

This is an interesting study, but does not prove that long-distance runners are more fertile or more attractive.

Ways to increase your fertility levels include stopping smoking, drinking alcohol in moderation and maintaining a healthy weight through healthy eating and exercise.