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Higher testosterone levels enable women to run for longer

Is it fair to let athletes with naturally higher testosterone compete as females without reducing their hormonal levels?

Louise Prime

Wednesday, 16 October 2019

Physically active, healthy young women whose testosterone levels were boosted were able to run for much longer before becoming exhausted than women given placebo treatment, although testosterone had no significant effect on any anaerobic performance measures, research has found. The authors of the small study*, published in the British Journal of Sports Medicine, also found that women given testosterone also gained muscle mass even though their overall body mass did not change – but they added that their results might not be generalisable to elite athletes.

Researchers led from the Karolinska Institutet in Sweden noted that rare differences in sex development (DSD) can cause some women to have a greatly increased production of testosterone, into the male range; that the prevalence of 46XY, DSD among elite female athletes is estimated to be about 140 times higher than in the general population; and that the International Association of Athletics Federations (IAAF) has faced criticism and legal challenge for stipulating that these athletes must lower testosterone levels to below 5nmol/l of blood to be eligible to compete at international level in middle-distance races (400m to one mile).

The research team randomised 48 physically active, healthy women aged 18-35 years to 10 weeks’ treatment with either 10mg of testosterone cream daily or to placebo, and investigated the effects on both aerobic and anaerobic performance. They also recorded changes in participants’ body composition. They found that:

  • Mean circulating levels of testosterone rose from 0.9nmol/litre of blood to 4.3nmol/l among the women given testosterone cream, with no change in the placebo group.
  • In tests of running time to exhaustion, there was a significant 21.17-second increase (8.5%) in the testosterone group compared with the placebo group.
  • Mean change from baseline in total lean mass was 923g for the testosterone group and 135g for the placebo group; mean change in lean mass in the lower limbs was 398g and 91g, respectively. Body weight changes were similar in the two groups.
  • The groups did not differ significantly on the secondary outcomes: average and peak power output (Wingate test – although this increased by a statistically non-significant 15.2W in the testosterone group compared with 3.2W in the placebo group) or muscle strength (squat jump, counter movement jump and knee extension peak torque).

The authors said their study’s strengths were its double-blind, randomised, placebo-controlled design, zero dropout rate, good adherence and use of gold-standard tests, but they acknowledged that it was limited by its short treatment duration and a dose of testosterone resulting in moderately elevated levels that were not in the male range. They commented: “For secondary outcome variables, the power to detect group differences may have been insufficient. Furthermore, the magnitude of the observed findings in our physically active women could not be directly generalised to an elite female population.”

But they pointed out that although women’s testosterone levels in the study did not reach those usually found in men, they were still enough to produce a significant improvement in running time to exhaustion.

They concluded: “The physiological effect of testosterone is the same whether the source of testosterone is exogenous or endogenous. Our results are therefore of great importance for the ongoing discussion of whether it is fair to allow athletes with naturally producing high testosterone to compete in the female category without reducing their hormonal concentration to the female range.”

*Hirschberg AL, Knutsson JE, Helge T, et al. Effects of moderately increased testosterone concentration on physical performance in young women: a double blind, randomised, placebo controlled study. British Journal of Sports Medicine, 2019. DOI: 10.1136/bjsports-2018-100525

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