Experimental Brain Research

, Volume 237, Issue 12, pp 3391–3408 | Cite as

Effects of arm weight support on neuromuscular activation during reaching in chronic stroke patients

  • Keith D. Runnalls
  • Pablo Ortega-Auriol
  • Angus J. C. McMorland
  • Greg Anson
  • Winston D. ByblowEmail author
Research Article


To better understand how arm weight support (WS) can be used to alleviate upper limb impairment after stroke, we investigated the effects of WS on muscle activity, muscle synergy expression, and corticomotor excitability (CME) in 13 chronic stroke patients and 6 age-similar healthy controls. For patients, lesion location and corticospinal tract integrity were assessed using magnetic resonance imaging. Upper limb impairment was assessed using the Fugl-Meyer upper extremity assessment with patients categorised as either mild or moderate–severe. Three levels of WS were examined: low = 0, medium = 50 and high = 100% of full support. Surface EMG was recorded from 8 upper limb muscles, and muscle synergies were decomposed using non-negative matrix factorisation from data obtained during reaching movements to an array of 14 targets using the paretic or dominant arm. Interactions between impairment level and WS were found for the number of targets hit, and EMG measures. Overall, greater WS resulted in lower EMG levels, although the degree of modulation between WS levels was less for patients with moderate–severe compared to mild impairment. Healthy controls expressed more synergies than patients with moderate–severe impairment. Healthy controls and patients with mild impairment showed more synergies with high compared to low weight support. Transcranial magnetic stimulation was used to elicit motor-evoked potentials (MEPs) to which stimulus–response curves were fitted as a measure of corticomotor excitability (CME). The effect of WS on CME varied between muscles and across impairment level. These preliminary findings demonstrate that WS has direct and indirect effects on muscle activity, synergies, and CME and warrants further study in order to reduce upper limb impairment after stroke.


Human Stroke Upper limb Muscle synergy Reaching Transcranial magnetic stimulation 



The authors acknowledge assistance provided by April Ren, Terry Corin, Fiona Doolan, and support from Saebo Inc. for supplying the SaeboMAS. WB received funding from the Health Research Council of New Zealand (Grant No. 14/136).

Supplementary material

221_2019_5687_MOESM1_ESM.docx (16 kb)
Supplementary material 1 (DOCX 16 kb)
221_2019_5687_MOESM2_ESM.pdf (1.9 mb)
Supplementary Fig. 1 Anatomical T1-weighted images in the transverse plane at the level of the lesion for each patient. Patient numbers correspond with Table 1 (PDF 1958 kb)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Movement Neuroscience Laboratory, Department of Exercise SciencesUniversity of AucklandAucklandNew Zealand
  2. 2.Centre for Brain Research, University of AucklandAucklandNew Zealand
  3. 3.Auckland Bioengineering Institute, University of AucklandAucklandNew Zealand

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