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What is the best material to use for a rearfoot post? Extrinsic rearfoot posts are important in the overall rearfoot control achieved with custom functional foot orthoses. However, no studies have demonstrated a significant advantage of one rearfoot post material over another (polypropylene, EVA, thermoplastic cork, etc.).
During the 1980's, many orthotic labs switched to softer materials, such as EVA and thermoplastic cork, because they were less expensive and easier to apply. But these materials degrade quickly as they wear, and they tend to round on the bottom, causing them to lose their stabilizing effect. Now, many labs are converting back to polypropylene rearfoot posts because of their durability and subsequent superior stabilizing effect. Polypropylene rearfoot posts rarely wear down or change shape during the life of the orthoses.
Some practitioners believe that the softness of EVA and cork diminishes shock at heel contact, especially for runners. However, advances in shoe design have significantly improved cushioning in athletic shoes, eliminating the need for additional cushioning in the rearfoot post. In fact, adding a cushioned rearfoot post could possibly reduce rearfoot stability.
What say you?
I am grateful to Larry & Paul @ ProLab who let us reproduce their communique's here.
I have always considered it somewhat paradoxical that we use a rigid piece of plastic to control a foots motion and then use a non-rigid (but firm) heel post to try and control the rigid piece of plastic .... my $0.02
I have often thought it odd that based on theory alone we think it is OK to try and hold the foot quite rigidly in one position when quite clearly the foot is a dynamic structure in it's entire evolutionary history.
I'm a bit of a fan of less rigid stabilizers, quite happy to replace EVA posts as required. I like to think that the foot can function into and out of the more efficient starting place we give it, rather than "lock it up and hold it there"
Regards Phill
Polyprop or EVA as a heel post?
Linear Mode
