Oscar Pistorius is a world class Olympic sprinter. He’s also a double, below-the-knee amputee. What allows him to compete is a grit that most of us can only imagine, along with a pair of Össur’s Flex-Foot Cheetah legs, J-shaped carbon fiber prostheses that fill in for feet and calves.

By now, you’ve surely heard of Össur legs and Pistorius’s watershed Olympics qualification. But what you may not know is a design problem that had to be solved first. Whereas every sprinter competes on spikes, Össur legs are smooth carbon fiber bands. So how do you affix spikes? By hand. Roughing up the surface, strong fixatives, and lots of brute force.

Even for a famous athlete of Pistorius’s resources, his spikes were a logistical nightmare that took two hours to replace. His trainers were worried about the ongoing impact of the Össur legs on his knees. And, because the spike work was totally manual, there was a lot of inconsistency on the fit of the tread (and thereby, the traction Pistorius could expect, especially during wet races).

Luckily, Pistorius is sponsored by Nike, and one of the perks of a Nike sponsorship is access to the first wave of technologically superior equipment. Tiger Woods can use prototype Nike drivers–clubs that hit farther and more controlled than others–because the top athletes in their fields get the really good stuff. For Pistorius, that meant Nike designer Tobie Hatfield chased the athlete down around the globe to create a newer, better Cheetah spike called the Nike Spike Pad.

“We were certainly able to take the learnings of spikes on shoes for 22 years, but obviously the difference is that we’re affixing it to a more immovable object, the carbon fiber blade,” Hatfield tells Co.Design. “It doesn’t articulate like a human foot does, so it was really really important for me to understand where he hit, his initial contact on the blade. Because it’s so stiff and rigid, we had to be very exact.”

So in Össur’s Iceland lab, Hatfield, along with Pistorius’s prosthetist, made Pistorius sprint again and again using Spike Pad prototypes on a pressure-sensitive treadmill–while also filming his foot strike at 500 fps. With Pistorius obviously unable to feel his feet to comment on the fit, they could only use Pistorius’s form as feedback, meaning these measurements were especially critical.

“We did that over three hours. He was pretty tired by the end,” laughs Hatfield. “I think the treadmill was fixed close to 20 mph. He’s a sprinter, not a marathon runner.”