Adaptation of multi-joint movements during postural disturbances

The objective was to investigate the adaptation of the multi-segmented body movements induced over time by vibratory proprioceptive stimulation of the calf muscles and by galvanic vestibular stimulation. Twelve normal subjects were with eyes open or eyes closed exposed to vibratory stimulation of two different amplitudes and frequencies, or to simultaneously applied galvanic and vibratory stimulation. Multi-input multi-output system identification methods as well as quantitative analysis were applied to the biomechanical experimental data of anteroposterior and lateral body movements and torques induced towards the ground. The immediate adaptive response to the stimulation onset was that the subjects adopted a more rigid posture with coordinated movements of primarily head-shoulder and head-hip body segments. The body-movement amplitudes at all measured sites as well as the amplitudes of the ground support forces decreased over time as a result of another, somewhat slower adaptation process. The subjects required more time to adapt to a rigid movement pattern when the subjects were simultaneously exposed to both galvanic and vibratory stimulation. Moreover, the accuracy of the MIMO model and correlation analysis between measured torque variance and head; shoulder; hip and knee movement variance suggests that force platform recordings reflect both in anteroposterior and lateral direction the body movements at these sites.