London — The governing body of world athletics on Wednesday welcomed a landmark study showing high testosterone helped women run better, saying it justified their decision to bar Olympic champion Caster Semenya from key races.
In a study in the British Journal of Sports Medicine, Swedish researchers found women with higher testosterone could run longer and had more lean muscle mass.
The International Association of Athletics Federations (IAAF) - which governs track and field - embraced the study as proof it had done the right thing in barring South Africa's Semenya for high testosterone levels, a primarily male hormone.
"The IAAF introduced a testosterone limit for the female category for the sole purpose of maintaining fair and meaningful competition for women," it said in a statement on Wednesday.
The study, it added, "reinforces our evidence-based conclusion that high testosterone levels give female athletes a significant advantage in some athletic events."
Medical professionals had believed that testosterone fuelled strength and endurance in men, but the benefits for female athletes were previously unclear.
No longer, according to the researchers from Karolinska Institutet in Sweden, and other institutions.
"Our study supports a causal effect of testosterone on physical performance, as measured by running time to exhaustion, in young healthy women," said the researchers, whose study was released on Tuesday.
There was no immediate reaction from Semenya, whose barring from the 800-metre race in September's World Athletics Championship sparked controversy in and outside of sport.
Her case became a test of where sports authorities draw the line when it comes to athletes whose bodies fall outside standard ranges or who change gender then seek to compete.
A 28-year-old double Olympic champion, Semenya has a medical condition called hyperandrogenism, which boosts her testosterone count. The athlete has refused to take hormone suppressing medication to comply with the regulations.
The hormone limitation was initially imposed earlier this year for intersex athletes whose bodies do not fit the usual expectations of male and female at birth, drawing condemnation from the United Nations.
On Tuesday in Qatar, the IAAF revamped the rule to add transgender competitors to the list of restricted athletes.
It had based its ban on evidence that it had partly funded and which drew criticism; scholars from the University of Colorado at Boulder said they could not replicate the study and found 17 to 32 percent of the data used was wrong.
This new study was conducted on 48 physically active women aged 18-35, with some randomly chosen to take a testosterone cream and others to take a placebo over 10 weeks.
Researchers tested the women by measuring their running time to exhaustion, as well as their performance on a stationary bicycle and muscle strength during squats and other exercises.
Scientists found the women in both groups had gains after the experiment. But those with higher testosterone chalked up better results, lasting 21.17 seconds longer than before and gaining 923 grammes of lean muscle mass, their weight unchanged.
Lean muscle mass allows for speed, strength and endurance.
Emma O'Donnell, a lecturer in exercise physiology at Loughborough University, questioned if the study might impact not only LGBT+ communities but all competitive athletes.
"These study findings also brings into question whether having a cutoff value for testosterone is a good thing. Might it encourage female athletes to take testosterone...?" she wrote in an email on Wednesday.
The study's authors said their results were "of great importance" to the discussion around Semenya's condition but were not immediately available for further comment.
Earlier this year, a Court of Attribution for Sport said while the testosterone regulation was discriminatory, it was "necessary, reasonable and proportionate" to protect "the integrity of female athletics."
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