The Duo is the perfect combination of lightweight feel in a max cushioned package. The blown rubber outsole, injection molded midsole and super thin mesh upper, combine to create a crazy fast, cushy, lightweight racing shoe. The Duo delivers Fit4Her Speed to the Max. FOOTSHAPE™ TOE BOXAltra's FootShape™ Toe Box allows the toes to relax and spread out naturally and the big toe to remain in a straight position for maxium stability and power. FIT4HER™The Fit4Her™ technology means we customize every women's shoe to the unique anatomy of the female foot. Read more…ZERO DROP™ PLATFORMEvery Altra shoe features a Zero Drop™ Platform that places the heel and forefoot the same distance from the ground for natural alignment and a low-impact landing. MAX-LT™The Max-LT midsole provides a firm, max cushion platform.