Muscular Strength Is Related To Neuroelectrical Indices Of Inhibitory Control

Abstract

Prolonged exercise/movement induces peripheral muscle fatigue (PF). PF affects the brain function, leading to a decrease in sport performance. However, the detailed neural mechanisms in motion control during PF are unclear. Neural activity for motor preparation processing is evaluated using contingent negative variation (CNV) of the electroencephalographic event-related potential. PURPOSE:The purpose of this study was to clarify the effect of PF on motor preparation processing using CNV. METHODS: Twelve subjects participated in this study. As an experimental protocol, we conducted recordings in the following order: CNV paradigm (Pre), hand grip exercise, and CNV paradigm (Post). CNV paradigms consisted of a warning stimulus (S1) and imperative stimulus (S2) paradigm. S1 (blue circle) and S2 (red circle) stimuli with an interval of 2 s were presented on a monitor approximately 1 m in front of the subjects. After S2, the subjects were asked to adjust their force level to match the 20% MVC target line as quickly and accurately as possible. As behavioral data, the reaction time (RT) for S2 and RT variability was evaluated. CNV was recorded at 5 electrodes (Fz, Cz, Pz, C3, and C4). The amplitudes of CNV were analyzed from 0.5 to 1 s after S1 as early-CNV, from 1 to 1.5 s as middle-CNV, and from 1.5 to 2 s as late-CNV. As hand grip exercise, the subjects gripped a hand dynamometer with 0-30% MVC gradual contraction and relaxation in order to cause PF. The degree of fatigue was evaluated by MVC after each set. RESULTS: MVC decreased from 33.1±4.8 to 25.3±6.0 kg (p < 0.001). RT variability was significantly greater in Post (65±12 ms) than in Pre (58±13 ms) (p < 0.05), while no significant difference in RT was observed between Pre (337±51 ms) and Post (343±34 ms). The mean amplitude of late-CNV was significantly larger in Post (-6.8±5.1 μV) than in Pre (-3.1±3.7 μV) at all electrodes (p < 0.05), but no significant differences in the mean amplitudes of early-and middle-CNV were observed. CONCLUSIONS: Our data suggest that PF affects movement variability rather than movement speed, and that it also amplifies neural activity in motor preparation processing.