

That impression did not diminish when I saw a prototype of the socks — or, rather, the sock. (Only one in each pair is blessed with intelligence.) At first glance, it's just a regular old cotton sock, but with a whitish, plasticy, curved band stuck to it via a pair of metal snaps. Look closer and you'll notice a discolored patch on the bottom, with a thread running up to meet the plastic band. The iPhone of ankle-wear, this is not.


Wool socks
Wool socks (Creative Crop/Getty Images)


On one level, it's like a Fitbit or Fuelband for your foot: It can count your steps, track your altitude, and tally how many calories you've burned while walking or running. It sends the data to an iPhone app, which can store your stats, plan your workout, analyze your progress, and give you audible alerts as you run. Because it's on your ankle, Macagno says it's more accurate than traditional fitness bracelets, which have to try to infer your steps based on your arm movements.


In short, Esposito figured out how to make fabric itself into — in essence — a variable resistor. The more force is applied to it, the more energy it conducts. So by sending an electronic signal from the ankle bracelet down through the chemical-treated fabric and back, the smart sock can gauge the amount of pressure you're putting on different parts of your foot with every jump. It can tell whether you're walking, jogging, sprinting, jumping up and down or just shifting your weight — and send that information to your iPhone in real time.

As a result, it can tell you more than just how much you're running. It can tell you how you're running. And that makes it attractive not only to fitness buffs, but to physical therapists and podiatrists. Instead of simply assessing a patient's foot once before fitting an orthotic device, they can watch it in action over time. “It's like having a movie rather than a picture,” Macagno says.

As Americans have started to move from plush, deeply cushioned running shoes to more minimalist footwear, Macagno says, many have failed to adjust their running style accordingly. The smart sock can detect which part of your foot is hitting the ground first, and how hard. If it's your heel, rather than your forefoot, it can trigger a warning from your iPhone app: “For the last 10 meters, you have been heel-striking. Please adjust your weight forward,” it intones. If you fall behind your target pace according to the app's metronome, it can say, “You're losing your cadence. Speed up now.”

