Abstract
This study evaluated the effects of voluntary arm movements performed during difficult movements on the excitability of spinal motor neurons in the contralateral arm after motor learning, using F-wave analysis. Sixteen healthy volunteers participated in this study after giving their written informed consent (average age, 26.3 ± 4.7 years). They were assigned at random to two groups of eight: a simple task practice group, and a difficult task practice group. They were asked to sit on a chair, and F-waves were elicited from the right abductor pollicis brevis during the movement task before and after each of three practice tasks performed by the left arm. The movement task and practice tasks were repetitive movements between two targets placed 200 mm apart on a desk. The subjects were instructed to accurately touch the targets with the tip of a pen. The size of the targets was 5 mm × 150 mm (width × length) for the movement task. In order to adjust the difficulty level of the practice tasks, the target size was changed as follows: 50 mm × 150 mm for task 1 and 5 mm × 150 mm for task 2. We found that the F/M amplitude ratio was significantly reduced after the difficult practice task compared with the pre-practice ratio. The results suggest that, following motor learning, the facilitation effects on spinal motor nerves in the contralateral arm were attenuated by localization of cortical regions or by the attenuation of sensory input.
