With the AliMed Viscoelastic Polymer Heel Cups shock forces are a product of mass (weight) and velocity (speed). If you can slow rebound velocity and alter its direction, you dampen and dissipate shock forces. Press your thumb into the center of a shock-absorbing heel pad or cup, then withdraw it rapidly. If the material recovers just in time for the next heel strike, it’s providing maximum shock-force reduction. If the material rebounds instantly, the shock force is absorbed by the skeletal structure. Computer generated, biomechanically engineered visco-flow control dampens and reduces heel strike rebound velocity. Heel strike shock waves are dispersed from vertical to horizontal. Sizing: Small, Men’s 5 to 6, Women’s 4-1/2 to 8 Medium, Men’s 6-1/2 to 8-1/2, Women’s 9 to12 Large, Men’s 9 to 14