Abstract: An athletic shoe has a sole with a rearfoot strike zone segmented from the remaining heel area by a line of flexion which permits articulation of the strike zone during initial heel strike of a runner. The line of flexion is located to delimit a rearfoot strike zone reflecting the heel to toe running style of the majority of the running population. In addition to allowing articulation of the rearfoot strike zone about the line of flexion, the sole incorporates cushioning elements, including a resilient gas filled bladder, to provide differential cushioning characteristics in different parts of the heel, to attenuate force applications and shock associated with heel strike, without degrading footwear stability during subsequent phases of the running cycle. The line of flexion may be formed by various ways including a deep groove, a line of relatively flexible midsole material, and a relatively flexible portion of a segmented fluid bladder.

Abstract: The invention is directed to a method for inflating a bladder including a first and a second distinct chamber linked in fluid communication by an interconnecting port, and a fluid fill inlet linked in fluid communication with the first chamber. A first nozzle set at a first predetermined pressure level and connected to a first fluid pressure source is inserted in the fill inlet to thereby inflate the first and second chambers to the first predetermined pressure. The interconnecting port is sealed to isolate the first chamber from the second chamber out of fluid communication with each other such that the second chamber is isolated at the first predetermined pressure. The first nozzle is removed from the fluid fill inlet. A second nozzle set at a second predetermined pressure level and connected to a second pressure source is inserted into the fluid fill inlet to thereby inflate the first chamber to the second predetermined pressure.