Abstract
In this study, desired center of pressure (dCOP) was introduced to evaluate dynamic postural stability. The dCOP is defined as a virtual point on the ground, where the moment around the body center of mass (COM) becomes zero when dCOP and the measured COP (mCOP) coincide. We hypothesized that, when the misalignment of the dCOP and mCOP (dCOP-mCOP) increases up to a certain value due to a large perturbation during walking, it becomes difficult to make a compensatory step and to recover balance of COM and to continue gait. Here we tested this hypothesis in slipping during turning. The study involved twelve healthy young adult males with an average age of 21.5±1.9 yrs. The subjects were asked to (1) walk straight and turn 60 degrees to the right with the right foot (spin turn) on a dry floor surface, and (2) walk straight and 60 degrees spin turn to the right on a slippery lubricated surface. The dCOP-mCOP during turning in the slip trial with fall were significantly larger, particularly in x-direction (i.e., the medial-lateral direction during straight walk), than that in no-slip trial and slip trial without fall. The receiver operating characteristic (ROC) analysis indicated that the dCOP-mCOP in x-direction is good indicator of falling (area under the curve (AUC) = 0.93) and the threshold in the dCOP-mCOP in x-direction to distinguish for fall or no-fall was 0.55 m. These results support our hypothesis in slipping during turning.
Highlights
The dynamic postural stability of the human gait has been attracting a lot of attention from many researchers
We presented that the subject was not able to continue gait, i.e. fell, when the desired center of pressure (dCOP)-measured center of pressure (COP) (mCOP) reached a certain value, in x-direction (Figs 7 and 8)
MCOP moved toward left-forward direction on x-y plane while dCOP was keeping moving right-forward on x-y plane resulting in a large deviation between mCOP and dCOP, especially in xdirection
Summary
The dynamic postural stability of the human gait has been attracting a lot of attention from many researchers. The majority of such biomechanical studies have focused on the relationship between the center of mass of the entire body (COM) and base of support (BOS) defined by the feet. Measures for assessing the dynamic postural stability have been proposed on the basis of the relationship between the COM and the BOS limit using an inverted pendulum model. Et al [2] proposed an extrapolated center of mass (XCoM), which is defined as the COM position with an addition of a linear function of the COM velocity and which must be positioned over the BOS to maintain postural balance during steady state walking. The margin of stability, which is the distance between the XCoM and the border of the BOS [2, 7], has recently been widely used as a measure of dynamic postural stability during steady state walking [8,9,10]
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