When it comes to the pinnacle of human performance and athletic achievement, humanity has yet to surpass one milestone: finishing a marathon in less than two hours.

Put another way: Neil Armstrong walked on the moon roughly half a century before anyone got close to a two-hour finish.

But thanks to a combination of knowledge on human performance and athletic technology, we're getting a much better idea of exactly what it will take to break the 2-hour marathon barrier, according to science—that is, how an elite runner like Eliud Kipchoge, who took home gold at the 2016 Rio Olympics in the men’s marathon, or Wilson Kipsang, the former marathon world record holder, can employ race-day strategies to shave every precious second from their time.

 

As for that athletic technology? Nike and Adidas, ever the archrivals, are competing in their own races to deliver the world's fastest times—Breaking2 for Nike and Sub2 for Adidas—and, therefore, the world's fastest shoes. Nike on Tuesday unveiled its Zoom Vaporfly Elite, while Adidas rolled out its announcement with the adizero Sub2.

Will the shoes make the world's fastest runners even faster? We'll see. But for now, here's what we know about the next generations of marathon footwear.