Influence of motor imagery of isometric thenar muscle activity under different muscle contraction strengths on spinal motor neurons’ excitability and cardiac sympathetic nerve activity

Abstract

[Purpose] This study aimed to determine the differences in spinal motor neurons excitability and autonomic nerve activity during motor imagery of muscle contractions of different contraction strengths. [Subjects and Methods] F-waves and the LF/HF ratio of 10 healthy subjects were recorded. F-waves and the LF/HF ratio were recorded at Rest1, 50%Image1, Rest2, 50%Image2, and Rest3, respectively. This experimental condition was called the 50% condition. For the 100% condition, F-waves and the LF/HF ratio were recorded using the same process. [Results] Persistence during the Image1 and Image2 trials under the two muscle contraction strengths was significantly greater than that in Rest1. The F/M amplitude ratios during Image1 and Image2 under 50% MVC were significantly greater than that in Rest1. The LF/HF ratios during Image1 under the two muscle contraction strengths were significantly greater than that in Rest1. The relative values of persistence, F/M amplitude ratio, latency, and LF/HF ratio were similar during Image1 and Image2 for the two muscle contraction strengths. [Conclusion] Motor imagery under voluntary muscular contractions of 50% and 100% increases spinal motor neurons’ excitability and cardiac sympathetic nerve activity. Differences in the imagined muscle contraction strengths are not involved in changes of spinal motor neurons’ excitability and cardiac sympathetic nerve activity.