The IAAF believes its new rules will “preserve fair and meaningful competition in the female classification” because female athletes with high testosterone have an advantage of up to 9% over women with normal levels of testosterone.
The move, which is sure to divide opinion, was unanimously approved by the IAAF council last month.
According to the world-renowned sports scientist, South Africa's Ross Tucker, the effect will be significant on athletes such as Semenya.
“If this policy passes, then I would predict that Semenya will be five to seven seconds slower over 800m,” Tucker wrote in a detailed analysis of the situation on Twitter.
“The other really interesting thing is that, guided by the new IOC transgender policy that lowers the upper limit for testosterone to 5nmol/L, the IAAF are setting their limit at 5nmol/L. It used to be 10. That will slow the times of these athletes down even more than it did in the past,” Tucker added.
Tucker told the Guardian: “History suggests Semenya will lose about four seconds to five seconds. Because in 2013 and 2014, when the IAAF were diligent about ensuring her compliance with the upper limit at that time (10nM), she was running 2:00. I don’t think she even qualified for the Commonwealth Games. Now, at 5nM, that effect will be even larger, I suspect. She will go from a 1:54 to 2:01-2:03, is my estimate.”
Semenya's personal best over 800m is in fact 1:55.16.
Semenya ran 1:56.68 to win gold at the 2018 Commonwealth Games. If Tucker is correct and Semenya would lose up to seven seconds, she would've finished last in the race - assuming she'd even qualified for the final in the first place.
For interest's sake, Semenya ran 1:55.28 in winning the gold medal at the 2016 Rio Olympics (again would've been last if seven seconds were added to her time), while in 2012 at the London Games she won in a time 1:57.23 (after Russia's Mariya Savinova was disqualified for doping) - and once again an extra seven seconds would've seen her cross the line in last place.