INFLUENCE OF MIDSOLE CONSTRUCTION AND UPPER VAMP DESIGN IN THE PRONATION MOVEMENT WHILE RUNNING

The relationship between the excessive rearfoot pronation and some injuries has been widely described in the literature (Bates, Cavanagh, Nigg, Stacoff). The influence of midsole design and material in the amount of pronation has also been analyzed by different authors. Nevertheless the relative influence of midsole and upper vamp design and their interactions have not been studied enough. The aim of the study presented was to investigate the relative effect of midsole material and thickness as well as upper vamp systems in controlling pronation. Twelve prototypes of running shoes were specially designed and constructed for this study. The prototypes corresponded to a factorial experiment design of the following factors: two midsole thicknesses, three midsole materials, and the presence or absence of an external heel counter and post. The materials selection was based on a previous study of the mechanical characteristics of a group of different Poliurethanes with different densities. The stiffness and energy absorbing capacity of the materials were previously studied by simulating impact loads of running by means of a dynamic testing machine. The external heel counter and post was selected as a representative of a very effective rearfoot control feature based in a previous study where it appeared to be the most effective system of the studied (heel counters, bondings for the lacing and internal posts). Three runners participated in the study. All of them were rearfoot strikers and hiperpronators. The experiences consisted of filming three right foot supports with two high speed cameras. Velocity of running was fixed at 12.8 Km per hour while velocity of filmation was fixed at 150 images per second. After digitizing the images obtained, a three dimensional study of the rearfoot movement was done. The results obtained can be summarized as follows: - Midsole thickness, midsole material and the presence of the heel counter showed significant influence on maximum rearfoot pronation with the most important being the midsole material in the range of variations of the study. - The material presenting low rigidity and low shock absorbing capacity was the one that showed higher pronation angles. - Higher pronation angles were found for the thicker midsoles. - The heel counter and post was found to have less influence on maximum pronation angles than the midsole thickness and material