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Liu, Xiyao

University of British Columbia

When balancing upright, humans must differentiate self-motion generated by their own motor commands from that induced by external events. This dynamic process is required to generate balance-correcting responses and must take into account uncertainty in the sensorimotor control of balance induced by sensorimotor noise as well as sensing and actuation delays. In the present study, I characterized how humans adapt their control of standing balance when faced with uncertainty associated with sensorimotor delays. Twenty-two young healthy adults stood upright individually in a robotic balance simulator that allowed me to manipulate the delays between their self-generated ankle torques and resulting whole-body motion. Participants balanced in the anteroposterior direction with baseline delays (10ms) and adaption to imposed delays of 250ms for 20 minutes. I observed that the introduction of sensorimotor delays destabilized how participants balanced upright, most falling frequently within the first 5 minutes. Participants also exhibited an increase in lower leg muscles activation (4-12 times compared to pre-adaptation), and agonist-antagonist co-contractions (5-13 times compared pre-adaptation), immediately after the delay was introduced. Through exposure to the imposed delays, participants adapted their control of balance by minimizing whole-body motion variability from 10.64 ± 3.47 to 1.19± 0.64 [°/s]². The sway velocity variance at the end of the adaptation was 15 times greater than post-adaptation quiet standing. Similarly, through the adaptation, the gradual decrease in the muscle activation and muscle co-contraction was also observed. When removing the imposed delay (post-adaptation period), the sway variance in the participants whole-body motion quickly return to pre-adaptation values. Muscle activation and co-activation at post-adaptation was also lower at the post-adaptation trials compared to those observed during the late adaptations. The present findings show that humans adapt their control of balance by increasing muscle activation and co-contraction when faced with imposed sensorimotor delays and exhibit minimal (or brief) after-effects in motion variability when an imposed delay is removed. The results from this study provide initial insights to help us understand how humans adapt to the changes in sensorimotor delays they may experience throughout their lifespan or encounter a neurological disorder.

Text

2024-01-08

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87160

Kinesiology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/