Simulations of human body during locomotion require a realistic representation of the foot which is the major interacting part of the body with the environment. Most simulation models consider the foot to be a rigid link, and impose unrealistic kinematic conditions. This study utilizes a viscoelastic sphere model with realistic properties, which can be used to represent the plantar surface of the foot during locomotion. The mechanical properties of the sphere are identified using experimental data on heel pads (Valiant, 1984). To check the validity of the model the results of the experimental study are reproduced by simulating the impact tests. Sensitivity analyses of the model parameters are carried out. The model is found to be insensitive to variations in stiffness and damping properties. The change in the thickness of the soft tissue, however, affected the maximum force of deformation proportionally. ii symmetrical pressure distribution for the sphere during impact is calculated. It is concluded that the viscoelastic sphere model, presented here, can be incorporated into a foot model to represent the plantar surface of the foot. (C) 1998 Elsevier Science Ltd. All rights reserved.