MeshImportedRubber soleSurface: Road. Differential: 0 mm. Altra? recommends those new to natural running and zero-drop footwear should transition slowly by wearing these on shorter runs and gradually building up to regular mileage. Altra Zero Drop? Platform:? Heel and forefoot are equal distance from the ground.? Promotes proper form to reduce initial impact.? Natural Achilles loading for enhanced propulsion.? 1:1 ratio naturally aligns feet, back, and body posture.? Weight-baHit the ground running in the Altra? Footwear Duo Racing Shoes.Ideal for running, road racing, speed work.Support Type: Natural.Cushioning: High-energizing cushioning.