Indoor non-air-conditioned environments widely exist in the summer high temperature weather. The work efficiency of the people who stay indoors for a long time is seriously affected by the indoor high temperature. In this paper, the changes of the circadian rhythms of work efficiency in indoor high temperature environments were studied. Ten healthy subjects (five males and five females) were selected in the experiments randomly. In each experiment day, the maximum hourly outdoor temperature was selected as 28 °C, 32 °C, 36 °C, and 38 °C, respectively, to determine the experiment conditions. In each experiment condition, subjects’ response time, accuracy rate, grip strength, work willingness, and physiological parameters were monitored for 24 consecutive hours. Meanwhile, the hourly outdoor temperatures of the experiment day were accessed from the weather report during the experiment. Then the cosinor method and statistical method were adopted. The results indicated that the response time, grip strength, and work willingness followed circadian rhythms. However, the accuracy rates of the Stroop color-word test (SCWT) and numeral inspection task (NIT) did not show an obvious circadian rhythm. The effects of high temperature on the circadian rhythms of grip strength and work willingness were mainly reflected in the decreases of the median and amplitude. The effects on the response time were mainly reflected in the decrease of the median. In addition, forehead temperature showed a significant negative correlation to response time, and it could be considered as a predictor to assess the level of work efficiency. This study gives an alternative method to replace direct measurement of the ability indices at work site and provides basic data of 24 consecutive hours, for showing changes in human work efficiency. It could be helpful to predict the low performance in advance to reduce occupational accidents.
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