An 'Effort Grunt' is the name given to the short gruff exhalation noises which people often make when exerting themselves.

The noises are not restricted to humans, and are heard in many other primate species (ref. ) - suggesting an early evolutionary trait.

There have been many attempts to explain the phenomenon. Some researchers suggesting that the grunts may somehow help with power efficiency - perhaps by increasing oxygen absorption. For example, some studies have shown that grunting can increase the speed of tennis serves (ref.). Whereas other studies with weight lifters showed that grunts don't appear to have any effect.(ref.)

Another theory is that the grunts date back to communications in a pre-speech time of human evolution - with a general meaning along the lines of "I need help with this" (ref.)

Note : There are suggestions that in certain competition sports, deliberately exaggerated grunts can be used to attempt to 'intimidate' opponents.