Effect of suspensory strategy on balance recovery after lateral perturbation

Postural stability is essential for performing daily activities and preventing falls, whereby suspensory strategy with knee flexion may play a role in postural control. However, the contribution of the suspensory strategy for postural control during sudden lateral perturbation remains unclear. We aimed to determine how suspensory strategy contributed to postural adjustment during sudden perturbation in the lateral direction and what knee flexion setting maximized its effect. Eighteen healthy young adults (10 male and 8 female) participated in this study. Kinematic data during lateral perturbation at three velocities (7, 15, and 20 cm/s) were collected under three knee flexion angle conditions (0 degrees, 15 degrees, and 65 degrees) using motion capture technology. Postural adjustments to the external perturbation were assessed by four parameters related to the temporal aspects of the center of mass (COM): reaction time, peak displacement/time and reversal time, and minimum value of the margin of stability (minimum-MOS). Our results showed that the COM height before the perturbation significantly lowered with increasing knee flexion angle. The COM reaction times for low and mid perturbation velocities were delayed at 65 degrees of knee flexion compared to 0 degrees and 15 degrees, and the COM reversal times were significantly shorter at 65 degrees of knee flexion than at 0 degrees and 15 degrees across all perturbation velocities. The minimum-MOS at the highvelocity of perturbation was significantly smaller at 65 degrees of knee flexion than at 0 degrees and 15 degrees. In conclusion, the adoption of a suspensory strategy with slight knee flexion induced enhanced stability during sudden external and lateral perturbations. However, excessive knee flexion induced instability.