Limits of Dynamic Balance Control Derived by Center of Mass Acceleration during Sit-to-Stand Movement

The purpose of this study was to establish a region of stability using the center of mass (COM) acceleration and characterize age-related differences in the control of COM in relation to the region during sit-to-stand (STS) movement. A single-link-plus-foot inverted pendulum model was used to determine boundaries of the regions of stability using COM velocity and acceleration (ROSv and ROSa). Ten healthy young and elderly adults [Young (Norm) and Elderly] were asked to stand up from a chair at self-selected natural speed. Young subjects were also asked to perform another block of trials with purposely bending their trunk prior to seat-off [Young (Bend)]. No significant differences among the three groups were detected in COM velocity at seat-off. However, peak COM acceleration differed significantly, suggesting that even though a similar momentum is observed at seat-off to achieve the STS task, the momentum is controlled differently prior to seat-off. The ROSa could serve as a complement to the ROSv, providing insights into how the COM is controlled prior to seat-off during STS movement.