Heel pad mechanics in shod conditions : Conflicting mechanics

Abstract

GROUND REACTION FORCES IN SPRINTING Michiyoshi Ae*, Ken Miyashita*, Shoitiro Ooki*, and Takashi Yokoi** * Institute of Health and Sport Sciences, University of Tsukuba **Industrial Products Research Institute Tsukuba City, Ibaraki 305, JAPAN The purpose of this study was to investigate the changes in ground reaction forces (GRF) during sub-maximum and maximum sprinting. Fourteen male sprinters and jumpers were asked to make contact with a Kistler force platform with the maximum and the sub-maximum (ca. 80%) speeds. The analog signals of three orthogonal components of GRF were recorded and converted to data equivalent to sampling rate of 400 Hz. Impact type vs non-impact type:8 distinct difference was found in the vertical component. Nine subjects were categorized as an impact type and five subjects as a nonimpact type. Continuous lateral force in the 2nd half was seen in the non-impact type while the impact type showed fluctuating medio-lateral force. Regardless of the types, double peaked anterior force and single peaked posterior force were observec. Effects of sprinting speed:The most remarkable effect of speed was found in the vertical component of the impact type, i.e. double peaked pattern for the sub-maximum speed and for the maximum speed single peaked pattern with no relative minimum and no distinguished thrust peak. Impulse and average force of the 2nd half and the magnitude of force at the midpoint were larger in the sub-maximum than the maximum speed. These results and geometry of the support leg for the impact type suggestea that the force exerted by the leg muscles, especially the plantarflexors was smaller for the 2nd half in the maximum speed than the sub-maximum speed.