We investigated the influence of the imagined muscle contraction strengths on spinal motor neuron excitability in healthy volunteers. F-wave was used for assessing spinal motor excitability. The F-waves during motor imagery (MI) under 10, 30, 50, 70, and 100% maximal voluntary contractions (MVCs) were compared. Furthermore, we investigated changes of the F-waves during motor imagery for 5min. Motor imagery under 10, 30, 50, 70, and 100% maximal voluntary contractions can increase spinal motor neuron excitability. However, the imagined muscle contraction strengths were not involved in changes of spinal motor neuron excitability. Additionally, spinal motor neuron excitability after 5min from onset of motor imagery returned to the rest level. Thus, in clinical use of motor imagery, slightly imagined muscle contraction strength is enough for facilitating spinal motor neuron excitability. Also, duration of motor imagery needs to be considered.

[Purpose] This study aimed to examine the effect of motor imagery on the accuracy of motion and the excitability of spinal neural function. [Subjects and Methods] Thirty healthy volunteers (males, 15; females, 15; mean age, 20.3 ± 1.0 years) were recruited. F-waves was recorded at rest, while holding a sensor, and while using motor imagery. Next, subjects learned 50% maximum voluntary contraction. The pinch force was measured without visual feedback before and after motor imagery. F-waves were analyzed with respect to persistence and the F/M amplitude ratio. Correction time and coefficient of variation were calculated from the pinch force. [Results] Persistence and F/M amplitude ratio ware significantly higher in the holding sensor and motor imagery conditions than in the resting condition. In addition, persistence under motor imagery was significantly higher than that in the holding sensor condition. No significant differences were observed in relative values of correction time and coefficient of variation between the two pinch action conditions. The pinch force in task 2 approximated a more authentic 50%MVC than that in task 1. [Conclusion] Motor imagery increases the excitability of spinal neural function, suggesting that it also affects accurate control of muscle force.

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Purpose: This study aimed to examine the effects of motor imagery on the excitability of spinal motor neurons and accurate motion. Subjects and Methods: About 30 healthy volunteers were recruited. F-waves were recorded at rest, while touching a sensor and motor imagery conditions. Also, the pinch force was measured before and after motor imagery. Furthermore, the subjects mastered the 50% MVC pinch force with learning times of 10 s, 30 s, 1 min, and 2 min beforehand. Results: Spinal motor neuron excitability with motor imagery after motor learning for 10 s, 30 s, 1 min, and 2 min was significantly increased as compared to other conditions. Accurate motion in the pinch task after motor imagery was better maintained than in the pinch task before motor imagery with motor learning times of 30 s and 1 min. However, with learning times of 10s and 2 min, the subject's ability to sustain accurate motion in the pinch task after motor imagery was significantly decreased as compared to that of the pinch task before motor imagery. Conclusion: Motor imagery increases spinal motor neuron excitability. To maximally improve accurate motion using motor imagery, it is important to practice and master motor learning beforehand

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F-waves are used to measure the excitability of spinal motor nerve function. This study aimed to investigate the F-wave patterns in a patient with cerebrovascular disease who had no voluntary movement of the hand, particularly the thumb, caused by a considerably increased tone of the thenar muscles. A patient with right hemiplegia caused by left cerebral hemorrhage (putamen) showed a considerably increased tone of the thumb flexors and no voluntary movements. F-waves were recorded from the affected thenar muscles with median nerve stimulation in the supine lying position during the first trial. Exercise therapy that included stretching of the affected thenar muscles was performed twice a week for 20 min for 8 months. Subsequent changes in the F-wave waveform were examined and considered as second trial. The latency and persistence of the F-wave and F-wave conduction velocity did not show any significant change between the two trials. Compared with the first trial, the F/M amplitude ratio in the second trial was increased. Following 8 months of exercise therapy, muscle tone improved slightly, and minimal voluntary movements of the affected thumb were noted. Since motor function of the affected thumb improved with exercise therapy but there was no improvement in F-wave data, it was determined that the main factor underlying the hypertonicity of the thenar muscles in this patient was more likely due to secondary muscle shortening than to spasticity. Unclear waves that possibly were F-waves were also observed approximately 20 ms after the appearance of the M-wave in the first trial but not in the second trial. Because exercise therapy showed muscle tone improvement and did not result in the appearance of unclear waves, F-wave patterns should be monitored for evaluating spasticity, which markedly increases muscle tone in patients with cerebrovascular disease.