Athletics’ governing body—the Court of Arbitration for Sport (Cas)—has ruled to limit female runners’ testosterone levels, following a legal challenge by 800m gold medallist Caster Semenya.

Two-time Olympian and three-time world champion, Semenya has unusually high testosterone levels, a condition called hyperandrogenism.

The International Association of Athletics Federations (IAAF) claims hyperandrogenism provides “significant competitive advantage.” It banned Indian sprinter Dutee Chand on those grounds in 2014.

Cas suspended hormone-restrictive regulation for want of evidence in 2015—but the IAAF then commissioned research to prove its point.

Today’s landmark judgement could justify future exclusions, based on differences in sex development (DSD), unless concerned athletes take long-term medication or undergo invasive surgery.

Scientists critical of the ruling argue DSD are no different to genetic mutations.

They cite renowned Olympic cross-country skier Eero Mantyranta, whose hemoglobin levels stood roughly 47% above male averages, meaning his blood carried more oxygen at high altitudes.

However, female athletes such as Briton Lynsey Sharp—who came sixth after Semenya in the 2016 Rio Olympics—insist letting biologically-advantaged runners compete creates “two separate races.”

Should the physical abilities of  “intersex” athletes be praised, as BBC reporter Megha Mohan suggests, just as “Usain Bolt’s height and Michael Phelps’ wingspan are?”

Or is testosterone suppression necessary to level the playing field?

Credit for this article's header image goes to Getty.