The role of the heel pad and shank soft tissue during impacts: a further resolution of a paradox

The aim of this study was to test the hypothesis that the motion of the sof t tissue of the lower leg contributes significantly to the attenuation of t he forces during heel impacts. To examine this, a two-dimensional model of the shank and heel pad was developed using DADS. The model contained a heel pad element and a rigid skeleton to which was connected soft tissue which could move relative to the bone. Simulations permitted estimation of heel p ad properties directly from heel pad deformations, and from the kinematics of an impacting pendulum. These two approaches paralleled those used in vit ro and in vivo, respectively. Measurements from the pendulum indicated that heel pad properties changed from those found in vitro to those found in vi vo as relative motion of the bone and soft tissue was allowed. This would i ndicate that pendulum measures of the in vivo heel pad properties are also measuring the properties of the whole lower leg. The ability of the wobblin g mass of the shank to dissipate energy during an impact was Found to be si gnificant. These results demonstrate the important role of both the heel pa d and soft tissue of the shank to the dissipation of mechanical energy duri ng impacts. These results provide a further clarification of the paradox be tween the measurements of heel pad properties made in vivo and in vitro. (C ) 2001 Elsevier Science Ltd. All rights reserved.