Previous studies employed thermal comfort or heatstroke risk indices (SET^*, WBGT, PET, etc.) to assess the outdoor thermal environment, and it was considered that people felt uncomfortable and the health hazard risk was high where such indices were higher than the threshold values. However, in urban streets, people often walk around and do not stay in the same place for prolonged periods. Thus, even when there are extremely hot points in the evaluation area, it is unlikely that these areas lead to the degradation of thermal comfort or health hazards if pedestrians pass through such points quickly. In this study, physical environments and human physiological responses were measured simultaneously to reveal the effect of radiant environments and human activities on human physiological responses.

 Field measurements were performed in pedestrian spaces within the premises of Tohoku University in the summer of 2016 – 2019 on 73 male subjects. The subjects wore clothes attached with instruments to measure the physiological variables (skin temperature, core temperature, heart rate, blood pressure, and amount of sweat) and walked with a cart attached with the instruments to measure the meteorological variables (air temperature, relative humidity, wind velocity, and short- and long-wave radiation).

 The cases were categorized into 4 types based on the mean radiant temperature (MRT) and state of human activity, i.e., (A) standing in a low MRT environment, (B) standing in a high MRT environment, (C) walking in a low MRT environment, and (D) walking in a high MRT environment. Additionally, the physiological responses of subjects who were walking in a high MRT environment and later made to stand in a low MRT environment were measured to evaluate the physiological responses when pedestrians rested in the shade of buildings or trees after walking in the sun.

 By comparing Types (A) and (C), we observed that the increase in skin temperature of the lower arm and back of the hand was small while walking in a low MRT environment. As these parts were not covered by clothes, they were considered to be strongly affected by the increase in convective heat loss while walking. Moreover, the increase in skin temperature while walking was large in the lower body. It was considered that the blood flow rate related to the heat transport increased in the lower body, i.e., the highly active part while walking. The increase in core temperature in Type (C) was larger than that in Type (A) because of increased thermogenesis while walking. By comparing Types (B) and (D), we observed that the increase in skin temperature of lower arm, and back of hand was small while walking in a high MRT environment. This is similar to that observed in a low MRT environment. In contrast, the increase in core temperature in Type (B) was larger than that in Type (D) in the low MRT environment. An increase in the amount of sweat and heat transported from the core to the skin due to increased blood flow rate during walking.

 For subjects who were walking in a high MRT environment and later made to stand in a low MRT environment, the rise in skin and core temperature declined owing to the low MRT environment and state of human activity from walking to standing, i.e., the decrease in the thermal load of pedestrians due to these effects.