title: Motor imagery muscle contraction strength influences spinal motor neuron excitability and cardiac sympathetic nerve activity.
abstract: [Purpose] The aim of this study was to investigate the changes in spinal motor neuron excitability and autonomic nervous system activity during motor imagery of isometric thenar muscle activity at 10% and 50% maximal voluntary contraction (MVC). [Methods] The F-waves and low frequency/high frequency (LF/HF) ratio were recorded at rest, during motor imagery, and post-trial. For motor imagery trials, subjects were instructed to imagine thenar muscle activity at 10% and 50% MVC while holding the sensor of a pinch meter for 5 min. [Results] The F-waves and LF/HF ratio during motor imagery at 50% MVC were significantly increased compared with those at rest, whereas those during motor imagery at 10% MVC were not significantly different from those at rest. The relative values of the F/M amplitude ratio during motor imagery at 50% MVC were significantly higher than those at 10% MVC. The relative values of persistence and the LF/HF ratio during motor imagery were similar during motor imagery at the two muscle contraction strengths. [Conclusion] Motor imagery can increase the spinal motor neuron excitability and cardiac sympathetic nerve activity. Motor imagery at 50% MVC may be more effective than motor imagery at 10% MVC.
authors.affiliation: Graduate School of Health Sciences, Graduate School of Aomori University of Health and Welfare, Japan; Clinical Physical Therapy Laboratory, Faculty of Health Sciences, Kansai University of Health Sciences, Japan.
authors.forename: Yoshibumi
authors.initials: Y
authors.lastname: Bunno
authors.affiliation: Clinical Physical Therapy Laboratory, Faculty of Health Sciences, Kansai University of Health Sciences, Japan.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Suzuki
authors.affiliation: Graduate School of Health Sciences, Graduate School of Aomori University of Health and Welfare, Japan.
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Iwatsuki
keywords: Autonomic nervous system activity; F-wave; Motor imagery
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