Research

Muscle weakness and lack of reflex gain adaptation predominate during post-stroke posture control of the wrist

Carel GM Meskers¹ , Alfred C Schouten² , Jurriaan H de Groot¹ , Erwin de Vlugt² , Bob JJ van Hilten³ , Frans CT van der Helm² and Hans JH Arendzen¹

¹  Department of Rehabilitation Medicine, Leiden University Medical Center, Albinusdreef 2, 2333 AL, Leiden, The Netherlands

²  Department of Biomechanical Engineering, Faculty of Mechanical Engineering, Delft University of Technology, Mekelweg 2, 2628 CD, Delft, The Netherlands

³  Department of Neurology, Leiden University Medical Center, Albinusdreef 2, 2333 AL, Leiden, The Netherlands

author email corresponding author email

Journal of NeuroEngineering and Rehabilitation 2009, 6:29doi:10.1186/1743-0003-6-29

Published:	23 July 2009

Abstract

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.

Conclusion

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.