Examination of trial-independent characteristics of body kinematics in response to similar postural perturbations

This study investigated the variability of certain kinematic features describing body segmental movement in response to a series of consecutive, translational movements of the supporting base along the anterior-posterior direction of the subject. These kinematic features included the amplitude and timings of the angular displacement, velocity and acceleration of the head, trunk, thigh and shank. A group of 21 subjects was tested, with their ages ranging from 22 to 77 years. The results showed that the amplitudes changed significantly from the first trial to the later trials in most of the variables observed. However, there existed certain features, other than the amplitude, that were invariant over consecutive trials. Specifically, the time at which the initial peak amplitude occurred, the onset time was found to be similar between trials.