The isoShift has an optimal blend of cushioning and guidance in a lightweight stability shoe. With a lively forefoot feel, superb cushioning, and the 1:1 Graduated Guidance System, this is the ideal shoe for runners looking for a lightweight, high performance stability shoe. 1:1 Seamless Race Upper creates an unparalleled fit with a seam free interior. 1:1 360 Lacing anatomically conforms to the foot for a tailored fit regardless of foot shape 1:1 Graduated Guidance System guides the foot from heel strike to toe off for a smooth, consistent feel 1:1 Energy Cell cushions the forefoot upon impact and then returns energy back to the runner. SKYDEX heel crash pad.