We all had some doubt from the moment we first saw her run. Does Caster Semenya have an unfair advantage over the rest of the women? Is she about to change the face not just of women’s 800m running but of women’s sport as a whole?

It was August 2009, and Semenya had just become the new face of South African running. In winning the World Championship 800m inside Berlin’s Olympic Stadium, she’d come from the proverbial nowhere, running 1:55.45, then the 13th fastest time in history. Still only 18, our doubt wasn’t so much over how easy it looked as it was her actual appearance.

What happened next needs little reminding: Semenya was subjected to some crude and invasive scrutiny, and with that ignited the slippery grey sporting gender debate – also known as the either/or debate, or simply the is she/is he debate.

Seven years on, however, that doubt is removed – for some of us. Now 25, Semenya will line up for today’s heats of the 800m (2.55pm Irish time) with an unfair advantage over the rest of the women, and with that the potential to change the face of Olympic sport.

Darker days

Because it’s not a question of if she will win (she will), but can Semenya break the world record of 1:53.28, which has stood since 1983 to Jarmila Kratochvilova of the former Czechoslovakia and the old darker days of doping. Even if she doesn’t break the record, her victory will reopen the question of why she’s being allowed to compete in a category of sport which by its very definition or classification is carefully protected.

"It's a ticking time bomb," Daniel Mothowagae, the veteran South African sportswriter, told the Guardian last month, and indeed the entire athletics world, especially the IAAF, might well be holding its collective breath come the final.

Why all this has happened may need a little reminding: after 2009, the IAAF found themselves defending leaked reports of gender testing on Semenya, which revealed she had no womb or ovaries but internal testes and high levels of testosterone, thus giving her that advantage over the rest of the women. Of course this wasn’t a straightforward process. The term “intersex” can apply to a range of variations in sex characteristics, someone who does not fit typical binary notions of male or female bodies.

In the wake of Semenya’s case in 2009, testosterone testing was introduced to identify cases where testosterone levels were elevated above an arbitrary level, termed hyperandrogenism. With that the IAAF introduced a sort of testosterone limit for women, requiring those over it to lower it with hormone treatment. The upper limit was set at 10 nmol/L, based on a study done on all the women competing in the World Championships in 2011 and 2013.

It actually found that 99 per cent of female athletes had testosterone levels below 3.08 nmol/L; so the upper limit of 10 nmol/L was three fold higher, to ensure the upper limit would apply only to those with hyperandrogenism (or else were doping).

Semenya’s performances, under this policy of reducing testosterone, dropped off. She never got close to 1:55.45, although she did win Olympic silver in London (behind a Russian women later implicated in doping), plus a World silver in 2011. At last year’s World Championships in Beijing, she failed to advance beyond the semi-finals.

Legal challenge

Around the same time, however, the IAAF policy on hyperandrogenism was legally challenged. Last July, Indian sprinter Dutee Chand won her case at the Court of Arbitration for Sport (CAS), who agreed with Chand’s lawyers that her high testosterone levels were entirely natural, and that the IAAF rule was discriminatory against women (given men don’t require testosterone testing); nor indeed are naturally tall basketball players – male or female – considered to have an unfair advantage. (The IAAF has until 2017 to appeal the finding).

So, just like that, Semenya was free again to compete without the required hormone treatment. Jean Verster, her coach, has carefully avoided commenting directly, just how much her re-elevated testosterone levels are having on her performances so far in 2016

“Caster does what she needs to do. Of course every now and then, as she’s only human, she would go through patches of feeling tired. Some days we had to do a little less.”

Verster actually puts her return to 2009 form down to simple lifestyle factors, a sort of older, happier Semenya. Last December, for example, she married long-term partner Violet Raseboya. He doesn’t need to say much more anyway – because Semenya’s performances now speak for themselves.

At the South African championships in June, she produced an unprecedented hat-trick – winning the 400m in 50.78 and the 800m in 1:58.54, both world-leading times for 2016, before winning the 1,500m, all within the space of four hours. It wasn’t the almost half-hearted effort of Semenya’s victories which raised eyebrows as much as her exceptionally lean yet strong appearance.

Victory

Semenya followed that with another 800m victory at the opening Diamond League meeting in Doha. She ran the last 100m in 13.6 seconds, winning in 1:58.26. No woman in the history of 800m running has run the last 100m faster than 13.6, at least not when going sub-two minutes on the process.

Then, in her last race before Rio, she ran a South African record of 1:55.33 in Monaco, the fastest time since 2008. She’s unbeaten all season, eight wins in eight 800m races and, according to the official IAAF race previews, is “red-hot favourite”, but who perhaps understandably don’t mention her hyperandrogenism.

Others however have been more forthright: David Epstein, writing for Scientific American last week, quoted philosopher Bernard Suits, who described sports as "the voluntary acceptance of unnecessary obstacles" – and Semenya's case is another reflection of that, given her extraordinary and anomalous genetic advantage.

South African sports scientist Russ Tucker, who has probably followed her case closer than anyone, has been equally clear: given women’s sport is a protected category, and that this protection must exist because of the insurmountable and powerful effects of testosterone, Tucker is adamant “that it is fair and correct to set an upper limit for that testosterone”.

Minority interests

There is still the question around proportionality, and how sport balances the interests of a minority. Others have questioned the actual effect of testosterone in athletes with hyperandrogenism, or to what degree it might give them advantage, given it may be utilised differently, although over 800m, even a 2 per cent advantage would mean the difference between winning gold and not making the final.

Others say that Semenya has won her right to compete in the courts, and that’s okay, but the athletes she competes against have rights too. If any athlete, through no fault of their own, has an unfair advantage over other athletes then it’s not a fair race, and Semenya is about to prove that beyond any doubt.