If you’re running a marathon despite knee pain, you might want to stop and think about some of your choices. Or at least slow the pace a little as you swing by the next aid station for sports drink and energy gel. But for runners with knee issues, you can see why the Vaporfly is an attractive shoe. Lightweight? Thanks to the ZoomX foam midsole, the Vaporflys come in under 7 ounces. Firm? The carbon plate inside the sole ensures a stable ride while amplifying the energy return. Fast feel? The people who regularly win marathons are buying Vaporflys (at $250!) faster than Nike can keep up with the production.