“The higher you go in terms of drop, the more you’re basically wearing a running-shoe version of a high heel,” Bowersock says. The average shoe has a 10- to 12-millimeter or higher drop, while more minimalist models have less or are even often zero-drop, or completely flat.
Although zero-drop shoes more accurately match the position of bare feet on the ground, transitioning to them too quickly can raise your risk of injury, Barnes says, likely because it stresses different muscles in your feet and legs than regular running shoes do. And if you’re prone to Achilles problems, a higher drop can take some of the pressure off your heel and calf, reducing your symptoms. (In fact, it’s similar to a treatment physical therapists recommend—sticking a foam pad under your heel.)
If you don’t have pain or a history of Achilles injuries, drop may be merely a matter of preference. If you tend to strike the ground with your heel first—a gait pattern common in newer runners—having a higher drop, and hence more foam under your heel, may feel better, Bowersock says. However, since there’s some evidence linking heel striking to injury, you might want to revisit that later on if you do develop pain in your legs or feet.
Carbon-fiber plates can make you faster—at a cost.
If you’ve been a regular racer itching for P.R.s, you’ve probably been following the controversy over carbon-plate fiber shoes like the Nike Vaporfly 4% ($ 250, nike.com) and NEXT% ($ 250, nike.com)—nearly all recent record-breaking performances in the running world, including Eliud Kipchoge’s sub-two-hour marathon, have been set in them. Other shoe companies also have models with carbon-fiber plates, like Hoka One One’s Carbon X ($ 180, hokaoneone.com).
In both Nike-funded and independent studies, including one that Barnes performed, the Vaporfly shoes have been shown to reduce the amount of energy you need to run by an average of 4% or more—which then translates into faster race times. The secret to how they work, Barnes says, has to do with the combination of foam and a thin, curved, carbon-fiber plate embedded within it.
The plate acts like a lever against the ground, propelling you forward with less effort. “Think of it as using a wrench versus your fingers to unscrew a bolt,” Paquette says. It also stabilizes the shoe, allowing manufacturers like Nike to pack more lightweight foam around it with less jiggling or side-to-side motion.
That foam is extra compliant—scientific speak for squishy—as well as resilient, or able to bounce back to its initial shape quickly. That means you lose less energy each time your foot hits the ground.
And as one study from the University of Colorado showed, your calf and foot muscles don’t have to work as hard with each step. That’s probably one reason runners often report that they feel less sore and are able to bounce back more quickly after a race or a hard workout when they’re wearing these shoes, Paquette says.
While some have suggested the technology only works for superfast runners, two New York Times analyses of Strava data—and, Barnes says, a study he’s completed but not yet published—suggest otherwise. “I’ve never measured a runner who didn’t show benefit running in the Vaporfly,” he says.
However, he says, they do represent a deviation from the idea of comfort: The foam is stacked so high many runners report feeling a bit unstable or gangly. And for the price, you could buy two pairs of most other models and rotate them, Bowersock says—a strategy that’s been shown to reduce injury risk.
The design of the uppers can make or break you in the blister department.
In recent years manufacturers have increasingly realized that what’s on top matters in the feel of a shoe too, Gray says. Now many use stretchy knit and woven fabrics with less stitching—some, like the Adidas Solar Boost ($ 160, zappos.com) or Brooks Launch ($ 100, zappos.com), are even all one piece. As a result they weigh less, hug your foot more snugly, and are less likely to rub your skin raw or cause blisters, Barnes says.