Paris, France: World athletics' governing body on Thursday introduced controversial new rules for female athletes who have high testosterone levels in a move seen as targeting South Africa's double Olympic 800 metres champion Caster Semenya.
The new rules will allow such athletes to compete only if they take medication to reduce naturally occurring levels of testosterone.
Semenya has long raised controversy because of her powerful physique and deep voice, as well as revelations of hyperandrogenism, the medical condition which causes a person to produce high levels of male sex hormones.
She replied to the new rules by retweeting messages of support and the slogan: "How beautiful it is to stay silent when someone expects you to be enraged."
The International Association of Athletics Federations (IAAF) has for years struggled to create a "level playing field" for female athletes while respecting Semenya's rights.
The South African has responded by winning one title after another -- most recently the 800m-1500m double at the Commonwealth Games.
The new rules, which the IAAF puts under the heading "Difference of Sexual Development" (DSD), cover races from 400m to the mile, including 400m, hurdles races, 800m, 1500m, one-mile races and combined events over the same distances.
Dr Stephane Bermon, of the IAAF Medical and Science Department, said in a statement: "The latest research we have undertaken, and data we have compiled, show that there is a performance advantage in female athletes with DSD over the track distances covered by this rule."
IAAF President Sebastian Coe said: "The revised rules are not about cheating -- no athlete with a DSD has cheated -- they are about levelling the playing field to ensure fair and meaningful competition in the sport of athletics."