Abstract
The effect of center of mass (COM) height on stand-still postural sway analysis was studied. For this purpose, a measurement apparatus was set up that included an accelerometry device attached to a rod: three plumb lines, positioned at 50, 75 and 100 cm to an end of the rod, each supported a plumb bob. Using a vice mechanism, the rod was inclined from vertical (0 degree inclination) in steps of 5 degrees to 90 degrees. For each inclination, the corresponding inclination angle was manually measured by a protractor and the positions of the three plumb bobs on the ground surface were also manually measured using a tape measure. Algebraic operations were used to calculate the inclination angle and the associated displacements of the plumb bobs on the ground surface from the accelerometry data. For each inclination angle, the manual and accelerometry calculated ground displacement were close. The height of COM, where the measurement was taken, affected the projected displacement on the ground surface. The COM height had a nonlinear double-effect relationship with sway as it can affect both the angle and projected sway. Normalization of the COM height was used to reduce this effect for comparison purposes.
Highlights
Postural sway during quiet standing is determined by the movement of the center of pressure (COP) position
The movement of COP under the feet regulates the center of mass (COM) of a person based on the operation of the inverted pendulum model [1]
In order to deal with the bias introduced by the COM height, the measurements could be normalized by setting the COM height to unity for all subjects
Summary
Postural sway during quiet standing is determined by the movement of the center of pressure (COP) position. In balance studies, during quiet standing, the COM sway can be used to determine the contribution of each sensory system, i.e., visual, somatosensory and vestibular, to postural control and to estimate their functionalities [4]. The use of accelerometry in human activity analysis and postural recognition has been reported in a number of studies [13,14]. Postural assessment can be carried out by measuring sway in stand-still position. The aim of this study was to demonstrate the effect of the COM height on postural sway analysis using an accelerometry-based approach of an inverted pendulum and to propose a method that allows sway comparisons across subjects with different COM heights to be carried out. An accelerometry approach for sway path measurement, the apparatus used in the study, and the results obtained are discussed
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