Evaluation of fatigue caused to human body by solar exposure by measuring brain function performance

Abstract

Following direct exposure to sunlight while pursuing leisure activities, many have noticed a strong sense of fatigue in the evening. In this regard, our results of a survey of awareness showed that the development of fatigue from solar exposure of the body was generally recognized. On the other hand, a tool for objective and quantitative determination of mental fatigue has recently been reported. Known as the Advanced Trail Making Test (ATMT), it is a method of evaluating brain function. In the present study, we attempted to determine fatigue development caused by exposure of the human body to solar radiation using ATMT results. For 3 days in the summer season, 15 male subjects (26–41 years old) received exposure to the sun equivalent to 100 kJ cm−2 of ultraviolet radiation three to four times each day. During the periods of exposure, the subjects wore short-sleeved shirts and short pants, and covered their heads with a towel. Following the 3-day period, they were divided into two groups based on their subjective evaluation of a sense of tiredness, fatigued (n = 10) and non-fatigued (n = 5). In the fatigued group, a significant increase in the subjective score for fatigue sense was observed in the evening of all 3 days following sun exposure, as well as in the morning of the third day, as compared with those in the non-fatigued group. Further, a significant increase in average ATMT value was also observed in the fatigued group in the evening of the first and second days following sun exposure, as well as in the morning of the third day. These results indicate that ATMT may be a useful evaluation tool for quantitative and objective measurement of mental fatigue caused by exposure to sunlight.