This paper presents a conceptual model for studying the contribution of each leg to sideways stability of a four-link biped. It was assumed that a linear feedback controller maintained balance with torque related to the deviation from a reference value of the angle made by the trunk with the vertical. Predictions for ground reaction forces produced in resisting sideways push at the pelvis, based on simulation using a simple linear controller, are presented for two special cases (using one or both legs). This simple model was then compared to experimental data in which participants were asked to resist a sideways push. It was observed that all participants employed a strategy in which one leg was used to develop the force response. With this simple model, it was possible to simulate different kinds of responses to the balance perturbation. This model could be considered the first step of a more complex model in order to include specific components related to physiological parameters.
G. Dietrich, Univ. of the Mediterranean, Science & Techn. Luminy 163, Case 918, 13288 Marseille Cedex 09, France; A.M. Wing and M. Gilles, Ctr for Advanced Studies in Sensory Motor Neuroscience, Univ. of Birmingham, Edgbaston Birmingham B15 2TT, UK; I. Nimmo-Smith, MRC Applied Psychology Unit, 15 Chaucer Rd, Cambridge CB2 2EF, UK.