(AP) -- In his biggest race, distance runner Jacob Riley might slip on a pair of shoes he's never even broken in.
The reason is simple: They're supposed to be fast.
Or so the research suggests on Nike's new Alphafly Next% sneaker. Riley, who has no shoe sponsor, wants to be able to go stride for stride with anyone wearing Nike's game-changing shoe, or any of its competitors, when he lines up Saturday at the U.S. Olympic marathon trials in Atlanta.
"It's an annoying decision to have to make this close to the race, but it is what it is," said Riley, who planned to test shoes up until race time.
No matter what times the marathoners turn in, or how well they run, they know that, after this race, the real headliner will be their shoes.
Which ones will cross first? Will it be the supposedly groundbreaking Nike Vaporfly or its next generation Alphafly Next%? Will it come from a Nike rival, several of which are desperately trying to close the gap? Or will it be a shoe without any of the new technology that just happens to be worn by a runner who is, quite simply, faster than the rest?
"Shoes are what's in the back of our minds right now," said Jared Ward, one of the race favorites. "Because it's what is in the front of the headlines."
World Athletics, track's governing body, recently outlined new guidelines to significantly tighten rules surrounding shoe technology. One of the stipulations is that any new shoe, in addition to being compliant, needs to be on the open market by April 30 if athletes want to wear them at the Tokyo Olympics this summer.
That's why so many shoe companies have been racing to launch enhanced models. Adidas, Hoka One One, Saucony and New Balance are among those that have recently released shoes featuring carbon-fiber plates for more spring and propulsion, similar to what Nike's created in its shoe lab.
Independent and Nike-sponsored studies have found that the shoe gives runners a 4% edge in energy efficiency.
"This has been such a controversial thing for our sport," Riley said. "Someone made the comment that it's changing the conversation away from the athletes, which is a little bit frustrating."
Riley doesn't think twice about stepping into shoes he's never tested out. If it feels good -- and feels fast -- he may wear the Alphafly version.
"Most people now, when (shoes) last 100 miles, would want them to be as fresh as possible to keep that spring as crisp as can be," Riley said.
Eliud Kipchoge of Kenya wore a prototype of the Alphafly when he ran the world's first sub-2-hour marathon in an unofficial race in October.
What's more, all three of the men's marathon medalists at the 2016 Rio Olympics laced up a version of the shoe, including third-place finisher Galen Rupp, who's among the favorites Saturday.
To some, the advances in the high-tech world of shoes remain an exciting revolution. Others have said it risks reducing marathons to a shoe competition.
The controversy prompted World Athletics to issue its most stringent shoe regulations in decades ahead of the Tokyo Games. The Vaporfly avoided a ban, and the debate rages on.
"It's not to knock any of those guys who run really fast in the Vaporfly," said Tyler Andrews, who's sponsored by Hoka One One. "They'd run really fast even if they were wearing Crocs."
Among the favorites in the women's race Saturday is Des Linden, who's sponsored by Brooks. Linden wrote on her social media page in January following the World Athletics announcement of their shoe restrictions: "BREAKING: @WorldAthletics rule all super shoes legal, with new requirement -- athlete must wear a foam red nose while using said shoes during competition. Many regulations on the foam nose to follow ..."
At 45, Bernard Lagat will try to make his sixth Olympic team as he switches over to the marathon. Granted, he's relatively new to the discipline, but he's a seasoned veteran -- and happens to be sponsored by Nike.
Riley realizes the attention is on the footwear. Should he earn one of the three men's Olympic spots while wearing Nike shoes over, say, Scott Fauble, who runs in Hoka One One, Riley understands how the conversation will go: It's gotta be the shoes.
"That would be aggravating and I don't think that tells the entire story," Riley said. "I'm glad to see that other shoe companies are going to have something out there so that we can quiet down that conversation."
When he's not running or training, Ward happens to be an adjunct professor at Brigham Young University in statistics. So this appeals to him: Working with his sponsor, Saucony, over the last year and a half to test out numerous shoe prototypes. That's why he feels confident at the starting line.
"I'm sure studies will be released after the trials with all these companies releasing new shoes," Ward said. "People will be comparing them and analyzing that question in a quantitative way to see how these shoes measure against one another. That's going to be fun science to wait for."