A forefoot Air Zoom unit helps you play on your toes and puts a pop in your first step. A heel Air Zoom unit provides support. Extra rubber in the toe area, specifically the big-toe side, adds durability. High-abrasion rubber in the forefoot offers durability and traction. We specifically designed the heel for rocker-like movements, like pulling back for a serve. Designed for wear on hard court surfaces With Air Zoom units and side-to-side stability, it’s made to unleash your inner might and smash whatever comes your way when it’s match point. Made for the best and those who aspire to be, the GP Challenge 1 helps you serve and swing with confidence. With Air Zoom units and side-to-side stability, it’s made to unleash your inner might and smash whatever comes your way when it’s match point.