The PUMA Foreverun Nitro uses an innovative new RUNGUIDE system to guide your stride through the most efficient gait, a system so unobtrusive that neutral runners could benefit on recovery days. Combining a purpose-built midsole and outsole geometry, with a stiffer heel clip, forefoot wrap and custom-built insole you get smooth and seamless guidance from first stride to last. NITRO cushioning offers a highly responsive feel underfoot with deep cushioning in two layers, the softer of which is next to the foot for high levels of comfort.