Testosterone suppression for transgender women has little effect on reducing muscle strength even after a year of treatment, according to new findings. Researchers say the findings could have important implications for transgender athletes in female sport.
Most sports governing bodies, including the International Olympic Committee, now have policies saying transwomen must take testosterone blockers for at least a year before they can compete at elite level.
But findings by the Karolinska Institute in Sweden, to be published this year, have shown the effect of the hormone treatment in relation to reducing leg muscle strength, is almost neglible for men who transition to become women.
That could be significant in sporting terms because it indicates the physical advantages of biological males are maintained even after transitioning and after hormone therapy to reduce testosterone levels.
Women’s rights groups have claimed for some time that trans women have an unfair physical advantage in some female sports.
Dr Tommy Lundberg, an exercise physiologist at the Karolinska Institute who has led the research, said that muscle mass dropped by five per cent after a year’s treatment, but that the effect on trans women’s muscle strength was neglible. The research was carried out on 23 volunteers — 12 trans women and 11 trans men — to monitor changes in muscle mass and strength during and after a year of hormone therapy.
Lundberg told The Times: “There has been no research at all previously on what happens, especially in terms of strength after transitioning. This is relevant for sports where strength is considered an advantage.
“We have found that trans women’s muscle mass decreases by five per cent after a year but they maintained their strength levels throughout the treatment period.
“While the people in the study are not transgender athletes, the data are still relevant to the sporting community given that there has been no data available on changes in lower-limb muscle strength at this point.”
Previous research has indicated biological males have at least a 10 to 12 per cent higher muscle strength than biological females, and in some power sports up to 39 per cent.
Lundberg’s research, which he has presented at several scientific conferences, also found that women who have transitioned to be men and taken testosterone saw their muscle strength increase by 15 per cent, but they were still not as strong as men who transitioned to be women and took the testosterone blockers.
Ross Tucker, a scientific researcher for World Rugby, believes sports may have to reassess their policies on transgender players as a result of the findings. He said: “Sports are going to have to move with a lot more caution on this.”
Last week, it was revealed that a transgender rugby player is aiming to play in the Welsh women’s league this season despite significant physical advantages.
Most sports now have policies that elite players who were born male and now identify as female must have testosterone below a certain level.
The IOC’s guidelines is 10nmol/litre for at least 12 months, while World Rugby has set a lower limit of 5nmol/litre.
The Times reported last week how the transgender cricketer Maxine Blythin, who is targeting a place in the England women’s team, has a batting average of 15.1 for Chesham 2nd XI men’s team — which is open to men and women — and 123 for the St Lawrence & Highland Court women’s team in Kent.
