**3.1. The autonomic nervous system during MI of isometric thenar muscle activity at 10 and 50% MVC**

#### *3.1.1. Purpose*

We previously suggested that MI can facilitate the spinal motor neuron excitability. Sympathetic nerve activity was increased during actual isometric muscle contraction [41]. If MI shares common neural substrates with motor execution, it would be expected to observe the similar pattern in autonomic nervous system (ANS) activity during MI would be observed. In previous research, the heart rate during MI was significantly increased than that at rest [42]. Thus, MI can regulate sympathetic nerve activity without any overt movement. However, whether the imagined muscle contraction strength affects the ANS activity is still unclear. Then, this research aimed to investigate the ANS activity during MI of isometric thenar activity at 10 and 50% MVC [40].
