The International Olympic Committee’s rule changes on transgender athletes have been applauded as a human rights victory. No longer will trans-females be required to have surgery. To take part in women’s events, they need only declare themselves female and keep their testosterone levels below 10 nmol/L for a year before competing.

Arne Ljungqvist of the IOC’s medical committee welcomed this as “more flexible and more liberal”. And it is great news — unless you are a woman athlete.

Testosterone levels in healthy men range between 7.5 and 25 nmol/L. Normal levels in women range from 0.20 to 3 nmol/L. So a male-to-female trans athlete will be allowed to have more than three times the upper range of this performance-enhancing hormone than a born woman. And