The 361 Spire 4 puts more spring in your run. A MORPHIT construction in the mid-foot and heel provides a more comfortable, secure and supportive environment for your feet. Along with a Pressure Free Tongue, that provides comfort and helps to avoid irritation during flexion. Additionally, Ortholite insoles utilize 20% recycled content while still retaining the performance fit and comfort that runners crave. The Spire 4 also features QU!K Spine which is a carbon fiberglass shank that adds linear integrity to the mid-foot. Also, the Spire 4 has benefits that help to provide a natural and balanced toe-off to enhance ground contact for better acceleration when you run!