Effects of monochromatic light on muscle fatigue and its recovery

Abstract

The present research was designed to examine whether monochromatic light exposure influences muscle strength output and muscle recovery after fatigue. Six male subjects performed a muscle fatigue task involving maximum voluntary abduction of the first dorsal interosseous (FDI) muscle in three sessions with 40 repetitions and test contractions of the FDI muscle with 8 repetitions during 30 min to assess recovery progress. Subjects also reported their general arousal level and mood state. There were four monochromatic light conditions in the present study, and we standardized measurement units of the light power as illuminance (red, green and blue I) and irradiance (red and blue II). We found that the root mean square (RMS) of the electromyogram (EMG) of FDI was significantly decreased during the muscle fatigue task, and it then increased during recovery. However, no significant difference was found among the four light conditions. The median frequency (MDF) of the EMG signal decreased significantly under the red light condition compared to that under the blue II light condition from the 15 min after completion of the muscle fatigue task to the end of recovery. Furthermore, the alpha wave band power ratio of the electroencephalogram (EEG) was found to be significantly increased during recovery under the red light condition. These results indicate that the short wavelength light (blue) may facilitate the recovery from muscle fatigue better than does the long wavelength light (red), and the long wavelength light decreases the arousal level of the cerebral cortex after a high-intensity muscle activity. The present study proposes a novel view of the research into monochromatic light effects on muscle activities.