Muscle weakness and lack of reflex gain adaptation predominate during post-stroke posture control of the wrist.
BACKGROUND
Instead of hyper-reflexia as sole paradigm, post-stroke movement disorders are currently considered the result of a complex interplay between neuronal and muscular properties, modified by level of activity. We used a closed loop system identification technique to quantify individual contributors to wrist joint stiffness during an active posture task.


METHODS
Continuous random torque perturbations applied to the wrist joint by a haptic manipulator had to be resisted maximally. Reflex provoking conditions were applied i.e. additional viscous loads and reduced perturbation signal bandwidth. Linear system identification and neuromuscular modeling were used to separate joint stiffness into the intrinsic resistance of the muscles including co-contraction and the reflex mediated contribution.


RESULTS
Compared to an age and sex matched control group, patients showed an overall 50% drop in intrinsic elasticity while their reflexive contribution did not respond to provoking conditions. Patients showed an increased mechanical stability compared to control subjects.


CONCLUSIONS
Post stroke, we found active posture tasking to be dominated by: 1) muscle weakness and 2) lack of reflex adaptation. This adds to existing doubts on reflex blocking therapy as the sole paradigm to improve active task performance and draws attention to muscle strength and power recovery and the role of the inability to modulate reflexes in post stroke movement disorders.
Meskers
Carel G M
CG
Department of Rehabilitation Medicine, Leiden University Medical Center, Leiden, The Netherlands. c.g.m.meskers@lumc.nl
Schouten
Alfred C
AC
de Groot
Jurriaan H
JH
de Vlugt
Erwin
E
van Hilten
Bob J J
BJ
van der Helm
Frans C T
FC
Arendzen
Hans J H
HJ
D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000368:Aged; D025461:Feedback, Physiological / Q000502:physiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology; D009128:Muscle Spasticity / Q000503:physiopathology / Q000534:rehabilitation; D018908:Muscle Weakness / Q000503:physiopathology* / Q000534:rehabilitation; D010291:Paresis / Q000503:physiopathology / Q000534:rehabilitation; D011187:Posture / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D012018:Reflex / Q000502:physiology*; D012021:Reflex, Abnormal / Q000502:physiology; D020521:Stroke / Q000503:physiopathology*; D000071939:Stroke Rehabilitation; D019415:Torque; D016474:Weight-Bearing / Q000502:physiology; D014955:Wrist Joint / Q000502:physiology*