Sensorimotor control of stability–movement transitions: impedance control dynamics at the human wrist
File(s)
Author(s)
Steadman, Nathan
Type
Thesis
Abstract
Mechanical impedance is central to human motor control, supporting postural stability, movement, and adaptation to uncertainty. In healthy motor behaviour it is usually treated as a brief corrective response, while persistence across motor contexts is mainly discussed in pathology. It therefore remains unclear whether impedance in unimpaired motor control is purely transient or can persist as an enduring control state between stabilisation and movement. There is also limited knowledge of the neural correlates, as most evidence is similarly derived in the context of clinical impairments such as Parkinson’s disease. This thesis addresses these gaps through a unified framework examining impedance across stability–movement transitions, integrating behavioural, muscular, and beta-band neural dynamics.
Using a robotic wrist manipulandum, impedance was elevated through stabilisation challenges altered in temporal predictability and perturbation amplitude. During stabilisation, impedance rapidly increased beyond passive mechanics and remained stable, indicating early formation of a stabilising control state. Changes in temporal predictability influenced impedance more than amplitude manipulations: uncertain scheduling of perturbations induced greater muscle co-contraction and importantly, this stabilisation-related impedance carried forward into voluntary movement, biasing movement dynamics and motor activity.
Neural analyses revealed strong suppression of beta-band corticomuscular coherence during stabilisation, with beta dynamics tracking stabilising demands and inversely coupling with passive stiffness, linking corticospinal activity to mechanical compliance. Post movement beta rebound showed context-dependent updating, with suppression following uncertain stabilisation. Passive stiffness assessments showed that changes in temporal predictability produced small but reliable shifts in stiffness persisting beyond task completion, whereas amplitude manipulations did not. Extending this analysis to Parkinson’s disease demonstrated quantified passive stiffness correlated with clinician-rated rigidity, supporting translational relevance.
Together, these findings provide evidence that impedance regulation in healthy motor control is not purely transient but a context-sensitive motor state persisting across task boundaries, sensitive to changes in temporal predictability, but not mechanical load.
Using a robotic wrist manipulandum, impedance was elevated through stabilisation challenges altered in temporal predictability and perturbation amplitude. During stabilisation, impedance rapidly increased beyond passive mechanics and remained stable, indicating early formation of a stabilising control state. Changes in temporal predictability influenced impedance more than amplitude manipulations: uncertain scheduling of perturbations induced greater muscle co-contraction and importantly, this stabilisation-related impedance carried forward into voluntary movement, biasing movement dynamics and motor activity.
Neural analyses revealed strong suppression of beta-band corticomuscular coherence during stabilisation, with beta dynamics tracking stabilising demands and inversely coupling with passive stiffness, linking corticospinal activity to mechanical compliance. Post movement beta rebound showed context-dependent updating, with suppression following uncertain stabilisation. Passive stiffness assessments showed that changes in temporal predictability produced small but reliable shifts in stiffness persisting beyond task completion, whereas amplitude manipulations did not. Extending this analysis to Parkinson’s disease demonstrated quantified passive stiffness correlated with clinician-rated rigidity, supporting translational relevance.
Together, these findings provide evidence that impedance regulation in healthy motor control is not purely transient but a context-sensitive motor state persisting across task boundaries, sensitive to changes in temporal predictability, but not mechanical load.
Version
Open Access
Date Issued
2024-11-11
Date Awarded
2026-03-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Haar, Shlomi
Vaidyanathan, Ravi
Tan, Huiling
Sponsor
Engineering and Physical Sciences Research Council
UK Dementia Research Institute
Grant Number
UK DRI-7003
UK DRI-7005
Publisher Department
Department of Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)