The purpose of this study was to investigate changes in the excitability of the contralateral upper limb spinal nerve function during movements of the fingers of different difficulties using F-waves. The F-waves of twelve healthy subjects were measured at rest and during two motor tasks: Task 1 involved flexion and extension of the left fingers at a frequency of 1 Hz, and Task 2 involved two-ball clockwise rotation using the left fingers, which is a difficult movement. The amplitude F/M ratio, appearance frequency, and latency of the F wave were analyzed. The appearance frequency was found to be significantly increased in Task 2 compared to at rest and in Task 1. There was no significant difference in the amplitude F/M ratio between the two tasks. The latency of the two tasks was also the same. The promotion effect on the contralateral spinal nerve function accompanying movement of the finger in one direction may increase in a difficult exercise task.
