*2.2.6. Results*

**2.2. The spinal motor neuron excitability during MI at 50 and 100% MVC**

**Table 5.** Comparison of F-wave among 10% MI, 30% MI, 50% MI, and 70% MI condition.

Relative values of latency 0.99 ± 0.02 0.99 ± 0.02 0.99 ± 0.03 0.99 ± 0.02

Our previous works [24–26] suggested that MI of isometric thenar muscle activity at 10, 30, 50, and 70% MVC can facilitate the spinal motor neuron excitability. However, the imagined muscle contraction strength did not influence on change of the spinal motor neuron excitability. Whereas, Cowley et al. [29] previously reported that the amplitude of H-reflex during MI of ankle plantar flexion at 100% MVC was significantly greater than that at 50% MVC. 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

**10% MI condition 30% MI condition 50% MI condition 70% MI condition**

1.53 ± 0.31 1.58 ± 0.61 1.78 ± 0.93 1.69 ± 0.45

2.40 ± 1.38 3.31 ± 0.56 2.52 ± 1.96 2.10 ± 1.37

Fifteen healthy volunteers were participated in this research (13 males, 2 females; mean age = 25.3 ± 5.0 years). All participants provided informed consent before the study commenced. This research was approved by the Research Ethics Committee at Kansai University of Health Sciences.

All recordings were conducted in accordance with the Declaration of Helsinki.

The environment and F-wave recording condition was set as previous works [24, 25].

For the rest trial (rest), F-waves were recorded during relaxation for 1 min. Subsequently, for the motor task, participants learned the isometric thenar muscle activity at 50% MVC (i.e., participants press the sensor of pinch meter by left thumb and index finger at 50% MVC) for 1 min. They were instructed to keep the 50% MVC value (kgf) measured numerically on the display of pinch meter. For the MI trial, participants performed MI of isometric thenar muscle activity at 50% MVC for 1 min. F-waves were recorded during MI (50% MI) and immediately after 50% MI trial (post) for 1 min respectively. The above process was defined as the MI at 50% MVC condition (50% MI condition). F-wave recording under 100% MI condition was performed using the same protocol as 50% MI condition. These conditions were performed

*2.2.1. Purpose*

Relative values of persistence

Relative values of F/M amplitude ratio

58 Evolving BCI Therapy - Engaging Brain State Dynamics

*2.2.2. Materials*

50% MI and 100% MI condition [28].

*2.2.3. F-wave recording procedure*

*2.2.4. Experimental protocol*

randomly on different days.

The persistence during MI under two MI conditions was significantly greater than that at rest (50% MI vs. Rest, 100% MI vs. Rest, \*\**p* < 0.01) (**Tables 6**, **7**). The persistence immediately after MI under two MI conditions was reduced to rest level (**Tables 6**, **7**).

The F/M amplitude ratio during MI under two MI conditions was significantly greater than that at rest (50% MI vs. Rest, 100% MI vs. Rest, \*\**p* < 0.01) (**Tables 6**, **7**). The F/M amplitude ratio immediately after MI under two MI conditions was reduced to rest level (**Tables 6**, **7**).

No significantly differences in the latency were observed among three trials (rest, MI, post) under two MI conditions (**Tables 6**, **7**).

The relative values of the persistence, F/M amplitude ratio, and latency did not exhibit significant differences between two MI conditions (**Table 8**).
