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Description

Includes data and code to replicate the figures and statistical tests from "Learning to stand with delays alters sensorimotor control but does not cause instability when returning to natural balance"

Abstract:
To maintain a bipedal posture, humans must compensate for inherent sensorimotor delays from neural conduction times and electromechanical delays. Aging and certain neurological disorders increase these delays; so, it is crucial that we adapt our control of balance to compensate for the uncertainty associated with acting on delayed sensory information. Although humans can adapt to imposed delays of 400 ms, the mechanisms underlying the adaptation process remain unknown because gross balance instability or errors are absent when returning to balancing without delays. To investigate this, we used a robotic balance simulator to impose delays of 250 ms while participants balanced upright. We characterized and modelled the adjustments in motor commands required to adapt to the addition and removal of delays. Following 20 minutes of adaptation, participants successfully maintained their balance with the imposed delay. When the delay was abruptly removed, participants remained upright with minimal changes in their whole-body oscillations, but we observed transient (5-20 s) increases in the spectral power between 1-2 Hz in the net ankle torques and lower limb muscle activity. Our model revealed that increased sensorimotor gains led to spectral changes in the balance motor commands. Our results indicate that increased sensorimotor gains are necessary to adapt balance control to longer delays and that these gains remained transiently elevated after the removal of the delays without resulting in postural instability. This highlights the remarkable adaptability of human balance control, revealing that the nervous system can flexibly adjust sensorimotor strategies to maintain balance under changing conditions.