Abstract
Mediolateral stability control during compensatory stepping responses is challenging for older adults but is critically important since lateral falls carry an increased probability of hip fracture. Previous work has found the orientation (eccentricity) and timing of the net ground reaction force (GRF) relative to the centre of mass (COM) to be important determinants of mediolateral stability recovery during the restabilization phase of the stepping response, following foot-contact. The present work sought to understand the individual limb contributions to stability recovery, by examining the eccentricity of the GRF generated by each limb during the restabilization phase of the stepping response. A lean-and-release paradigm was used to evoke stepping responses amongst 5 younger females (18-25 years) and 5 older females (>65 years) participants. Whole-body COM kinematics and GRFs beneath both limbs were quantified using motion analysis and four force platforms. Kinematic instability was quantified as the difference between the peak lateral COM position and the final stable COM position. Spearman's correlations were used to understand whether the magnitude and timing of GRF eccentricity from both the stance and stepping limb were related to kinematic instability during restabilization. Greater kinematic instability was related to a reduced peak and longer time-to-peak eccentricity of the stepping limb GRF immediately (<100 ms) following foot-contact. Greater instability was also related to a reduction in the secondary peak GRF eccentricity from the stepping limb, approximately 250 ms following foot-contact. These results suggest a principal role for the stepping limb in mediolateral stability control during restabilization following balance perturbation.Acknowledgments: Funding for this research was provided by the Manitoba Medical Service Foundation and the Natural Sciences and Engineering Research Council of Canada (NSERC).