A sole assembly for an article of footwear comprises a midsole, a sole
having a heel region, and a first wave spring disposed within a vacuity
located within the heel region. The wave spring includes a top surface
and a bottom surface. A plate, resting upon the top surface of the wave
spring, is unsecured to the midsole and sized to permit movement within
the vacuity along with the wave spring responsive to a rolling
footstrike.