Effect of Repeated External Perturbations on the Reflex Control of Human Posture — Influence of Reflex Delay, Duration and Gain

Abstract

The aim of the study was to assess the effects of muscle responses on the trunk motions during repeated perturbations by external forces. Patients with low back pain have delayed muscle reflex latencies to perturbations compared with healthy controls. The perturbation provoked trunk accelerations were simulated by a model consisting of four rigid bodies and six force elements representing trunk and hip muscles. The influence of the muscle responses were assessed by varying the reflex delays, the reflex durations, and the reflex gains. Trunk accelerations can be reduced by the simulated muscle responses. The optimal solution is not the result of extreme values of the reflex delay and duration range but of intermediate values. The relationship between the trunk accelerations and the reflex delay and duration respectively can be described by asymmetrical u-shape functions. As patients with low back pain showed delayed reflexes, their trunk motions are probably increased compared with healthy subjects.