Issue link: https://viewer.e-digitaledition.com/i/918219
72 runninginsight.com ©2017 Formula4media LLC. other zones stretch, and how that interacts with the forces on the bottom—it's all one thing." Kurt Stockbridge, footwear development VP at Skechers Performance, agrees. "It's much more holistic than people know," Stockbridge says. "It's not about this and that, but how everything comes together. Comfort: you can't define it—it is everything." Moving Parts At the very basic level, the upper's task is simple. "The primary purpose of an upper, where it can't fail, is to hold you on the footbed," says Stockbridge. "The rest is all bonus. It should contribute to doing that in the most comfortable way possible." Complicating this seemingly simple task is the fact that the shape of the foot changes as it moves through the stride. The midfoot arches and elongates with each step. The ball splays and flexes. The toes lengthen. Muscles all around the foot contract and relax. "The variables are just massive," says Tom Garza, product VP of global footwear at 361°. "There are a ton of moving parts, and the foot operates completely different for everybody. How do we allow mobility to occur, but provide structure at the right places?" The first key to creating this dynamic fit is to know where you want to hold and where you want to give. Experts and designers agree that the primary location you need control is in the midfoot. "If you can lock down the fit over the navicular—the instep—everything else kind of works," says Gray. Stockbridge defines the key location more precisely as just behind the ball of the foot. They point to a sandal or flip-flop strap as a simple example of where the foot needs support to keep aligned on the sole during stance and push-off. Importantly, however, this hold cannot extend forward around the ball of the 361° SPIRE 3 Jacquard engineered mesh pro- vides distinct zones of flexibility and support and eliminates the need for overlays. While the simpler upper adapts closer to the foot and lets it move more naturally, it still has an inner layer of soft webbing around the midfoot to hold the foot secure.