The South African faces having to take medication to lower her testosterone levels after athletics’ governing body the IAAF ruled it gives her an unfair advantage.
The IAAF has said females with above-normal or male equivalent levels of testosterone will have to change events or race against men unless they take medication.
But Semenya has opted to fight against the ruling, calling it ‘unfair’.
“It is not fair. I just want to run naturally, the way I was born,” she said.
“I am Mokgadi Caster Semenya. I am a woman and I am fast.”
The rule is due to come into force on 1 November, and it applies to women who race in track events from 400m up to a mile.
Testosterone is a hormone that increases muscle mass, strength and haemoglobin, which affects endurance.
South Africa's ruling party denounced the ruling as 'racist' and others have called it a 'witch hunt' against the athlete.
Law firm Norton Rose Fulbright, leading Semenya’s challenge, said in a statement that they would challenge the ruling in Lausanne on Monday.
They said: “Ms Semenya, like all athletes, is entitled to compete the way she was born without being obliged to alter her body by any medical means.”
Semenya, who is a two-time Olympic champion and three-time world champion, has not been far from controversy since her teenage success in the 800m at the 2009 world championships in Berlin, where the pure power of her surge to victory sparked questions and remarks about her sexuality.
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