Caster Semenya is hoping to make the difference for her country South Africa, as the chase for medals enters its final day.

The World 800m champion on Friday won the women 400m in a blistering pace finishing at 49.96 to set a new South African record. And in the 800m today she is in frame to clinch it.

“I’ve run 400 meters previously, I just haven’t really done it at competitive level,” Semenya said. “But for me it’s not about who I’m running against, it’s just about me doing what I can do best.”

We’re using this more for preparation for the 800. I feel good, that’s the main thing. I can’t wait until the 800 tomorrow (today).”

The 27-year-old Semenya who is believed to have a condition that produces high level of testosterone, could be stopped from competing in distances from 400 meters up to the mile after the IAAF introduced new rules barring women with high levels of naturally occurring testosterone from those events unless they reduce their testosterone levels. The rules come into effect November 1.