Caster Semenya and Oscar "Blade Runner" Pistorius train at the same Pretoria club in their native South Africa.
On Saturday, both step into the glare of the world's track and field spotlight -- and resumed public scrutiny -- to compete among a world-class field of competitors at the Prefontaine Classic in Eugene, Ore.
Each is the focal point for intriguing debate that transcends track and field. Newcomer Semenya's startlingly easy 2009 World Championship gold in the 800 meters, along with her chiseled appearance, triggered a storm over privacy, gender classification and gender determination.
Pistorius, who runs on carbon fiber legs after being born without both fibulas, is trying to become the first amputee sprinter to compete in the Olympics. Experts have clashed on whether the blades give him an unfair advantage, raising the issue of technology's intrusion on sport.
This will be the first time Semenya, 20, races in the U.S., as she prepares to defend her world title in South Korea in August.
Semenya, 18 at the time of her breakthrough gold, was barred from competition for 11 months, wiping out nearly all of her 2010 season as the sport's authorities clumsily -- and at times insensitively -- investigated. They eventually cleared her to race, but not before painful and humiliating rumors spread and details leaked about the teenager's gender tests.
In April, track and field's international governing body, the International Association of Athletics Federations, adopted guidelines written by IAAF experts and the International Olympic Committee's medical commission putting limits on the level of male hormones a female athlete can have and still compete.
They ruled female athletes with hyperandrogenism, a condition involving excessive androgens (male hormones), could still compete if the level was below the male range. Leeway is allowed if the level was higher but the athlete showed "an androgen resistance, which means that she derives no competitive advantage from such levels," according to an Associated Press report. How "competitive advantage" would be determined is still a question.
Those with unusually high androgens and not enough resistance would be banned from competition unless surgery or hormone-lowering drugs could diminish testosterone levels.
Pistorius also had to fight red tape for his green light to run. First banned by the IAAF to compete in able-bodied competition (Pistorius has dominated Paralympics races), he fought successfully to have the ban overturned but then failed to make the 2008 Olympics.
Both face more challenges to get where they want to be. At the Prefontaine meet, Pistorius will run in likely the best field he's ever faced, one that includes two-time Olympic gold medalist Jeremy Wariner and other U.S. Olympic medalists Bershawn Jackson, David Neville and Angelo Taylor.
Winning is almost out of the question. He'll try harnessing the fast field to make the world "A" qualifying time of 45.25 seconds. Pistorius' personal best is 45.61, good enough for "B" qualifying, which could get him in depending on who else makes it.
But Pistorius, the No. 3-ranked 400 runner in South Africa, wants his fate in his own hands.
"I've got a bit of work ahead of me, which I'm looking forward to," he told Sports Illustrated.
Semenya's return to the big time -- a week after Eugene, she'll compete in a meet in New York -- is coming with small steps. Some of that can be attributed to her working on qualifying for the 1,500 meters along with the 800 at worlds.
This season, she has run just one race outside her home country, winning the 800 in Senegal last weekend with a time of two minutes, 0.61 seconds, 13th-best in the world this year and five seconds slower than her world championship run (1:55.45). Now, after nearly two years in limbo, Semenya can begin the chase anew.