Core Body Temperature
noun - The core body temperature is the operating temperature of a human, specifically in the deep structures of the body such as the liver, in comparison to the temperature of peripheral tissues. This optimum temperature is 36.8°C (98.2°F) through it varies regularly as controlled by one’s circadian rhythms. Temperature examination in the rectum is the traditional standard measurement used to estimate core temperature.
The swimmer finished the race, but her core body temperature had dropped significantly and she was experiencing hypothermia.