This study investigates the varies in human physiological response, subjective sensation and acute subclinical health symptoms with increasing activity levels at different high temperatures. Thirty-two healthy subjects were recruited to walk on a treadmill in a climate chamber at a speed of 4 km/h. They experienced four temperature conditions (26 °C, 30 °C, 33 °C and 37 °C), each exposure lasting 85 min. Eardrum temperature, heart rate, skin temperature, systolic blood pressure, respiratory flow, and respiration rate changed significantly with increasing temperatures. At temperature of 37 °C, the SpO₂ decreased significantly compared with at 33 °C. Subjects perceived the environment unacceptable at 37 °C. The perceived air quality and air freshness correlated linearly with the enthalpy of air. The intensity of headache, dizziness, fatigue and sleepiness increased with increasing temperatures, while only aggravated significantly at 37 °C. Additionally, compared with the results at light activity level, heart rate and other key physiological parameters increased significantly with increasing activity levels. The subjects felt “very hot” at 37 °C, and the change trend in symptoms reported by subjects increased significantly at 37 °C with the increased exposure time, while no significant change was observed in 26-33 °C. It indicates that exposure to 37 °C impairs the health and safety of heat acclimatized subjects. Using linear fitting curve to predict human physiological tolerance time suggested by ISO 9986. The result shows that eardrum temperature exceeded 38.5 °C for 97min continuously walk at 37 °C. This provides valuable information involved physiological and psychological responses when human exposed to high temperatures in daily life or industrial production.

本研究调查了在不同高温下随着活动水平的增加，人体生理反应、主观感觉和急性亚临床健康症状的变化。招募了 32 名健康受试者以 4 公里/小时的速度在气候室中的跑步机上行走。他们经历了四种温度条件（26 °C、30 °C、33 °C 和 37 °C），每次暴露持续 85 分钟。鼓膜温度、心率、皮肤温度、收缩压、呼吸流量和呼吸频率随温度升高而显着变化。在 37 °C 的温度下，SpO ₂与 33°C 相比显着下降。受试者认为 37 °C 的环境是不可接受的。感知的空气质量和空气新鲜度与空气的焓呈线性相关。头痛、头晕、乏力和嗜睡的强度随温度升高而增加，而仅在 37°C 时显着加重。此外，与轻度活动水平的结果相比，心率和其他关键生理参数随着活动水平的增加而显着增加。受试者在 37°C 时感到“很热”，受试者报告的症状在 37°C 时随着暴露时间的增加而显着增加，而在 26-33°C 没有观察到显着变化。这表明暴露于 37 °C 会损害热适应受试者的健康和安全。使用线性拟合曲线预测ISO 9986建议的人体生理耐受时间。结果显示鼓膜温度超过38.5°C，在37°C下连续行走97分钟。这提供了有价值的信息，涉及人类在日常生活或工业生产中暴露于高温时的生理和心理反应。