Exercise alone can be hard, but exercising in the heat is a whole lot harder. Put simply, this is due to the balance between how much heat the body generates and how much it is capable of losing.
Human core body temperature typically remains around 97.7 to 98.6 degrees Fahrenheit (36.5 to 37 degrees Celsius), with small fluctuations across the day. Larger changes above 104 degrees Fahrenheit (40 degrees Celsius) can be dangerous.
Fortunately, humans are relatively well-adapted to dealing with the heat. One theory is that humans evolved a survival advantage as hunters because they could outlast animals that were less able to manage long periods of exertion under hot conditions.
How Do We Regulate Our Temperature?
1. Radiation: There are so many small blood vessels in the skin that, in total, they can receive up to 60 percent of output from the heart at rest.
As blood flows from the core of the body to the skin, opening of these small blood vessels allows more surface area for heat exchange with the environment.
Radiation of heat occurs when the surrounding environment is less hot than the skin surface. At rest in a cool environment, 60 percent of heat loss is by radiation.
