Wouldn't it be great if you could throw your body into neutral halfway through a 10K and just coast? That's a bit of the benefit of Adidas Springblade, which replaces the typical EVA midsole with a series of 16 thermoformed polymer blades. The Springblade's individually shaped fins (thicker at the heel, thinner in the midfoot) act like leaf springs, compressing on landing and, unlike EVA, translating the energy forward on every follow-through stride. One downside: weight. A men's size 9 weighs 12.8 ounces, though if the fins catch the public's imagination, you'll likely see lighter race iterations in the future. [$180; adidas.com]