Analysis of postural sway strategies using an inverted pendulum model and force plate data

The purpose with this study was to develop a simple method for analysis of postural movement strategies in the sagittal plane. The main idea was to utilise force components measured with a force plate in order to estimate both the input and output of an inverted pendulum model, and thereby determine the used balance strategy. The acceleration of the centre of mass is estimated with the model and compared with the true one (the ground reaction force divided by the body mass). The two accelerations must be in agreement if the body behaves like an inverted pendulum (the ankle strategy). Practical experiments demonstrated that tests where only the ankle strategy was used could clearly be separated from tests where non-ankle strategies were used.