Joint Reaction Forces during the Recovery of Postural Balance of Human Body

Abstract

The purpose of this study was to calculate three dimensional angular displacements, moments and joint reaction forces (JRF) of the ankle joint during the waist pulling, and to assess the ankle JRF according to different perturbation modes and different levels of perturbation magnitude. Ankle joint model was assumed 3-D ball and socket joint which is capable of three rotational movements. We used 6 camera motion analysis system, force plate and waist pulling system. Two different waist pulling systems were adopted for forward sway with three magnitudes each. From motion data and ground reaction forces, we could calculate 3-D angular displacements, moments and JRF during the recovery of postural balance control. From the experiment using mass-falling perturbation, joint moments were larger than those from the experiment with milder perturbation using air cylinder pulling system. However, joint reaction forces were similar nevertheless the difference in joint moment. From the results, we could conjecture that the human body employs different strategies to protect joints by decreasing joint reaction forces, like using the joint movements or compensating JRF by distributing the forces on surrounding soft tissues. The results of this study provide us important insights for understanding the relationship between balance control and ankle injury mechanism.