Eli5: how come our body heat increases during exercise?


While working out our body sweats to cool us down but shouldn’t the blood in our body also? With our blood flowing even faster during this period shouldn’t it be cooled by the sweat/air around us and cool our muscles from within?

In: 1

The body is roughly 20-25% efficient at converting food energy to muscle motion, so when we exercise there is a lot of extra heat to get rid of.

Exercise doesn’t cool you down. Your body is trying to cool you down on the outside because it’s doing its best to counteract the heat generated by the exercise, and because evaporative cooling requires access to the atmosphere. Your blood is picking up heat from your inside and hopefully dumping it outside if your sweat does a good enough job.

Remember, exercise uses a lot of energy, and your body gets energy from literally burning things. And because you’re a mammal, you’re mostly designed to keep that heat in. So when there’s too much heat, your body has to try to fix it.


*The byproducts of aerobic exercise = CO2 + H2O + heat.* Aerobic exercise is any solid state cardio (like jogging, biking or walking).

*The byproducts of anerobic exercise = lactic acid & heat.* Anaerobic exercise produces the “burning sensation” (lactic acid). It usually refers to high-exertion exercises like boxing, weightlifting or sprinting. When your muscles start to “burn” during weightlifting, or your legs start to “burn” when you run up stairs or during sprints, that is the lactic acid building up.

Basically all exercise eventually leads to heat as a byproduct (among other things). So your body temperature tends to increase anytime you perform any sort of exercise.