Thermoregulation

Working muscles produce heat as well as movement. Your body exchanges heat through contact, moving air or water, radiation and sweat evaporation. When heat production and environmental heat gain exceed heat loss, stored heat increases.

The same workout can therefore feel different in a cool gym and a hot, humid room. Pace, clothing, airflow, sunlight and the length of the session all change the conditions. Fatigue also has other causes, including the demands of the task, sleep and prior training. Feeling tired does not tell you your core temperature.

Before starting, check the setting and the work you intend to do. Build a plan around the session you actually have, with realistic breaks and cooling options. If conditions change, update the plan rather than assuming the original outlook still applies.