Final answer:
The subject of this question is Exercise Physiology, which deals with extreme heat stress and its impact on the body's temperature regulation.
Step-by-step explanation:
The subject of this question is Exercise Physiology. Extreme heat stress, where the body temperature is less than the environmental temperature, is a phenomenon related to the physiology of the body during exercise and physical activity. High body temperatures can affect the body's ability to regulate heat and can lead to heat stroke or other heat-related illnesses.