Talent, not testosterone, is behind the success of intersex athletes such as Olympic champion Caster Semenya, scientists said on Wednesday, stepping into a toxic battle of the sexes over fairness in sport.

Their editorial in the British Medical Journal flies counter to those who want to ban competitors with high levels of testosterone from competing in women-only events, and comes days before a key ruling on Semenya's eligibility to run.

Activists on one side of the debate say high testosterone in some athletes who are born with indeterminate sex powers them to victory and leaves women disadvantaged in their own events.