This is the 5335th most frequent Russian word.
остывания
"Остывания" means "cooling" or "cooling down."
Here, 'остывания' is used to refer to the process in which the water loses heat and its temperature drops.
Температура воды снижается из-за ее остывания.
The water temperature is decreasing due to its cooling.
In this sentence, 'остывания' describes the body's return to a normal temperature after exertion.
После долгой пробежки я почувствовал процесс остывания своего тела.
After a long run, I felt the cooling process of my body.
Here, 'остывания' indicates the drop in air temperature which results in a physical change.