From stochasticism to determinism in evaluation of human postural responses

Abstract

The Center of Pressure (COP) signal is a kind of human postural response and it is an established indicator of human ability to maintain balanced posture. Its form of the statokinesigram has complicated profile, which suggests stochastic or chaotic nature of COP movement. Here is presented developed statokinesigram trajectory (DST) as a basis of method for human postural response analysis. Since DST does not show signs of stochastic behavior it is suitable for modeling with help of linear system theory. In this study, volunteer's postural responses were affected by bilateral vibration stimuli of Achilles tendons. This vibration stimulus causes nonlinear response in anterior-posterior direction. DST allows to analyze this phenomenon through mathematical model in form of a transfer function. Its estimated parameters are useful in evaluation of human posture control.