Excitability of spinal motor neurons during motor imagery of thenar muscle activity under maximal voluntary contractions of 50% and 100%

Abstract

[Purpose] We often perform physical therapy using motor imagery of muscle contraction to improve motor function for healthy subjects and central nerve disorders. This study aimed to determine the differences in the excitability of spinal motor neurons during motor imagery of a muscle contraction at different contraction strengths. [Subjects] We recorded the F-wave in 15 healthy subjects. [Methods] In resting trial, the muscle was relaxed during F-wave recording. For motor imagery trial, subjects were instructed to imagine maximal voluntary contractions of 50% and 100% while holding the sensor of a pinch meter, and F-waves were recorded for each contraction. The F-wave was recorded immediately after motor imagery. [Results] Persistence and F/M amplitude ratio during motor imagery under maximal voluntary contractions of 50% and 100% were significantly higher than that at rest. In addition, the relative values of persistence, F/M amplitude ratio, and latency were similar during motor imagery under the two muscle contraction strengths. [Conclusion] Motor imagery under maximal voluntary contractions of 50% and 100% can increase the excitability of spinal motor neurons. Differences in the imagined muscle contraction strengths are not involved in changes in the excitability of spinal motor neurons.

The Application of Motor Imagery to Neurorehabilitation

“…The imagined muscle contraction did not affect the change of the sympathetic nerve activity. This is very similar with the result of the spinal motor neuron excitability during MI at various imagined muscle contraction strengths [24][25][26]28]. If central command during MI affects the sympathetic nerve activity via the corticospinal pathway, the imagined muscle contraction strength may affect the sympathetic nerve activity.…”

“…Then, we hypothesized the MI of isometric thenar muscle activity at 100% MVC will be greater than that at 50% MVC. In this research, we compared the spinal motor neuron excitability between 50% MI and 100% MI condition [28].…”

The Effect of Motor Imagery on Spinal Motor Neuron Excitability and Its Clinical Use in Physical Therapy

“…We investigated spinal motor neuron excitability during MI of isometric thenar muscle activity under 10, 30, 50, 70, and 100% MVC [13,14,19]. As a result, MI of isometric thenar muscle activity can facilitate spinal motor neuron excitability.…”

“…From the results of our previous work [13,14,19], MI of isometric thenar muscle activity under 10, 30, 50, 70, and 100% MVC can facilitate spinal motor neuron excitability. Furthermore, the imagined muscle contraction strength is not involved in changes of spinal motor neuron excitability.…”

“…Alternatively, the influence of duration of MI on the changes of spinal motor neuron excitability is not apparent. In our previous work [10,13,14,19], participants were asked to perform MI for 1min. Thus, this research aimed to investigate the influence of MI for 5min on spinal motor neuron excitability by analyzing F-waves.…”