The ankle strategy for postural control--a comparison between a model-based and a marker-based method

When analysing postural control statistical characteristics of the centre of pressure or the ground reaction force are often used. A complement would be to analyse movement strategies as well. The purpose of this study was to determine to what extent the ankle strategy is used to maintain the balance in standing. One important question is if it is sufficient to use only force plate data in this determination, or if markers have to be used. To answer this question we studied two different methods--a marker-based method and a model-based method. The latter needs force plate data only as input to an inverted pendulum model. Different measures were calculated and used to draw conclusions of to what extent the ankle strategy was used. Experiments demonstrated that the data from the two methods provided the same general conclusions, although there were some differences in the estimated measures. By using the model-based method instead of tracking markers we can increase the clinical effectiveness considerably, get a lesser amount of data, and still get results comparable to the marker-based method.