Control and stability of the complex inverted pendulum models in application to postural sway analysis of the vertical human stance

Mechanism of balance control is investigated on computerized posturography data on the vertical two–legged and one–legged stances measured on healthy subjects and the patients with osteohondrosis and coxarthrosis. Oscillations of the center of mass over 30 s of keeping the quiet stance and the trajectories for a step forward off the force platform have been computed. It was shown that during the one–legged stance the balance control strategy includes ‘scanning’ of the larger area with bigger sway amplitudes in the vicinity of the stable state as compared to the two–legged stance. A generalized model of the body as a multi–link system is proposed. Mass and inertia of each body segment and torques in joints are taken into consideration. The calculated own and forced frequencies of the model correspond to the spectral analysis of the posturography data. One–legged stance is proposed as a proper test for revealing the balance disorders. It is shown that investigation of the oscillations and trajectories of the center of mass for the step forward off the force platform is perspective for medical diagnostics to distinguish between the spine and joint pathologies. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)