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.
Impacts of normobaric/hypobaric hypoxia on physiological and subjective responses were examined in resting eight healthy young males at a low environmental temperature of 17 °C. They were exposed to the sea level maintained at 27 °C as baseline and then to the three experimental conditions which were combination of barometric (Pe) and partial oxygen (O2) pressures; normobaric hypoxia (NH, Pe= 760 mmHg and O2= 87 mmHg), hypobaric hypoxia (HH, Pe= 418 mmHg and O2= 87 mmHg), and normobaric normoxia (Control, Pe= 760 mmHg and O2= 159 mmHg). Temperatures of rectum (Tre) and 10 sites of skin surface(Tsk), oxygen consumption were measured. Finger-tapping test was performed to assess manual performance. Thermal sensation and subjective shivering activity were also evaluated. A significant difference in the Tre was not seen during exposure to the aimed test condition. On the other hand, a significant difference in the Tsk was observed, the Tsks in both the HH (28.5 ± 0.6 °C) and the NH (27.8 ± 0.5 °C) indicated higher value than that in the Control (27.2 ± 0.7 °C). Despite of larger temperature differences between the Tsk and the environment in the HH and the NH, the heat loss from the body in the HH (87 ± 23 W/m2) was significantly smaller than that in the NH (105 ± 19 W/m2). This is because the convective thermal resistance from the body increases with the decreasing atmospheric pressure so that the convective thermal resistance in the HH was larger than that in the NH. As the consequence, decline in the manual performance was suppressed in the HH and voted score of the subjective shivering was also statistically higher in the HH than in the NH, even though the O2 in air was identically kept at the low level in both the HH and the NH.