Strength of trans women drops slightly after year of treatment, research claims

• Loss of lean body mass around 5% after testosterone blockers
• Study raises questions for sport related to safety and fairness

Men have a greater performance advantage over women in cricket, golf and tennis compared to sports such as running or swimming according to new research, which also finds that testosterone blockers taken by transgender women only minimally reduce the biological advantage underpinning performance.

The study, published in Sports Medicine, found that while elite men are around 10-13% faster than elite women at running and swimming, the gap is between 29% and 52% when it comes to bowling cricket balls, hitting long drives, weightlifting and in sports that generally rely more on muscle mass and explosive strength.

“Performance differences larger than 20% are generally present when considering sports and activities that involve extensive upper body contributions,” the study adds. “The gap between fastest recorded tennis serve is 20%, while the gaps between fastest recorded baseball pitches and field hockey drag flicks exceed 50%.”

However when transgender women suppress testosterone for 12 months, researchers found that the loss of lean body mass, muscle area and strength was only around 5%. Therefore, they say, “the muscular advantage enjoyed by transgender women is only minimally reduced when testosterone is suppressed” and “small compared to the baseline differences”.

The results are significant because under the current International Olympic Committee guidelines, transgender women are allowed to compete in female sports categories if they suppress their testosterone below 10 nmol/L for 12 months before and during competition.

Yet even when testosterone was suppressed to around 1 nmol/L it did not “remove the anthropometric and muscle mass/strength advantage in any significant way” – although the authors say the reduced cardiovascular performance may generate smaller retained advantage in endurance sports.

The study raises significant questions for sport, with the paper stating “the IOC may need to reassess” whether its current guidelines for transgender women are fair or safe for female competition. They also ask whether, from a medical-ethical standpoint, it is acceptable for the IOC to ask trans women to significantly reduce their testosterone if it does not deliver on its stated aims.

Meanwhile researchers also found the biological gap between women and men is so great that 10,000 males have personal-best times that are faster than the current Olympic 100m female champion, as does the 14-year-old male schoolboy 100m record holder.

“These data overwhelmingly confirm that testosterone-driven puberty, as the driving force of development of male secondary sex characteristics, underpins sporting advantages that are so large no female could reasonably hope to succeed without sex segregation in most sporting competitions.”

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