When people lift something heavy, they often shout. Does shouting really make us stronger? In one study, 50 people squeezed a hand tool as hard as they could. First, they did it in silence.

Then, they did it while shouting a martial arts cry called a kiai. With the shout, they were about 7% stronger. This was true for both experts and beginners. So shouting is not just for fun.

Many athletes shout or grunt when they use their full strength. A 2012 study tested whether this actually helps. Fifty people, half of them martial arts experts and half beginners, squeezed a handgrip both silently and while shouting a kiai. On average, they were about 7% stronger when they shouted, and the effect was similar for both groups. This idea is not new.

In 1961, the Japanese physiologist Michio Ikai reported that people produced more force when they shouted at the moment of effort. He suggested that the brain usually holds back some strength to protect muscles and joints. A 2021 Japanese study found signs that shouting may weaken this "brake" in the brain.

Lifting a heavy box, lunging in kendo, or hitting a tennis serve, people often let out a shout at the moment of maximum effort. Research suggests this habit is more than a ritual. In a 2012 study, 25 experienced martial artists and 25 novices squeezed a handgrip dynamometer both silently and while performing a kiai. Average force rose from about 408 to about 437 newtons, an increase of roughly 7%, and the benefit appeared regardless of expertise. As early as 1961, the Japanese physiologist Michio Ikai reported that shouting, a sudden pistol shot, or hypnosis could raise maximal strength, leading to the idea that the brain normally imposes a protective limit on force.

A 2021 Japanese study supported this view: shouting not only increased grip force but also enlarged the pupils and, according to responses to magnetic stimulation of the motor cortex, reduced motor inhibition. However, these were small to medium-sized experiments comparing conditions within the same participants, and it is difficult to rule out the influence of expectations, since people may try harder when they believe shouting should help. A separate line of research suggests that tennis grunts may also make it harder for opponents to judge the ball.