Boosting women's testosterone can increase muscle mass and endurance

(Reuters Health) - Artificially raising women’s testosterone levels may result in improved physical performance, boosting endurance and muscle mass, a new study finds.

In a double-blind, randomized, placebo-controlled trial, researchers found they could improve young women athletes’ abilities by having them smear a cream containing testosterone on their thighs for 10 weeks, according to the results published in the British Journal of Sports Medicine.

“Our study gives evidence for the causal effect of testosterone on physical performance in women,” said the study’s lead author, Dr. Angelica Linden Hirschberg, a professor in the department of women’s health at the Karolinska Institutet in Stockholm. “Testosterone levels increased more than four times but were still much below the male range. The improvement in endurance by the increased testosterone levels was more than 8%.”

The report comes on the heels of a recent ruling that upheld the International Association of Athletic Federations’ regulations that require female athletes with naturally high levels of the hormone, such as the Olympic 800-meter champion Caster Semenya, to medically reduce their testosterone levels to be allowed to compete as women in middle-distance events.

One of the big unknowns has been the impact of testosterone levels on female athletes’ performance.

To answer that question, Hirschberg and colleagues recruited 48 healthy, physically active women aged 18 to 35 and randomly assigned them to apply either testosterone cream or a placebo cream for 10 weeks.

The researchers then tested the volunteers’ testosterone levels and their endurance. They also tested the women’s performance on a treadmill, leg power during stationary cycling and muscle strength during squat jumps, standing vertical jumps and tests of knee strength.

“The normal female range of circulating testosterone is 0.1 to 1.8 nmol/L and the normal male range is 8 to 30 nmol/L, so there is no overlap at all,” Hirschberg said in an email. “In our study, the testosterone group reached a mean testosterone level of 4.3 nmol/L, which is higher than the normal female range, but still lower than the male range.”

Endurance in the testosterone group was significantly higher: running time to exhaustion on the treadmill was 21.17 seconds longer – an 8.5% increase - in those with higher levels of the hormone. Women in the testosterone group also ended up with bigger increases in lean body mass: 923 g versus 135 g.

While the study proves that in the short term, at least, higher testosterone levels can lead to better performance in women, “the results could not be directly translated to female elite athletes with high testosterone in the male range,” Hirschberg said. “Our population were not elite athletes, but well-trained.”

The study design used by the researchers is “the gold standard,” said Dr. Andrea Dunaif, a professor and system chief of endocrinology and diabetes at the Mount Sinai Health System in New York City. “And it’s important as it relates to the controversy around the IAAF regulations for female athletes.”

Before this study, there was no solid scientific research proving that testosterone could improve female performance, Dunaif said.

Hormone levels in the testosterone group were in the range of what can be seen in a common medical condition called polycystic ovary syndrome, Dunaif said. “It’s well below the normal male level,” she added. “What I found absolutely remarkable was that they found a significant increase in endurance (with a relatively small increase in testosterone level).”

The new study was conducted “to see how much of a role testosterone plays in athletic performance in women,” said Dr. Gerald Montano, medical director of the Gender and Sexual Development Program at the UPMC Children’s Hospital of Pittsburgh.

“They did show that women who received testosterone performed better,” Montano said. “But that still leaves open the question of whether it’s fair for someone who is producing more testosterone to compete.”

There are many inborn factors that affect a female athlete’s speed and endurance, Montano said. “For example, the type of muscle a woman inherits may affect how much hemoglobin she produces and yet we don’t require a modification,” he added. “Drugging would be a whole different issue. But if someone is naturally producing more testosterone I think they should be allowed to compete.”

SOURCE: British Journal of Sports Medicine, online October 15, 2019.