Stabilographic analysis of unconstrained standing.

Natural standing is characterized by postural changes and several hypotheses have been proposed to explain these changes. In this paper, four hypotheses were investigated by quantifying the number of postural changes in the centre of pressure data from unconstrained standing in different experimental conditions, studying the effects of mechanical loading, visual conditions, and type of support surface and sole of the shoes. The subjects stood for 30 min with no specific instructions other than not to step off a force plate. There were no significant effects on the number of centre of pressure patterns associated with the postural changes due to load, vision, surface and shoes during standing; on average, approximately two centre of pressure patterns per minute were observed in all conditions. The analysis of the centre of pressure data by the commonly used statistical parameters (standard deviation, velocity, and mean frequency of the centre of pressure displacement and area of the stabilogram) also did not reveal any effect of the different conditions.