Calming their nerves... when I get nervous, I get all pent up and sometimes difficult to breathe. A shout and sudden expelling of air helps me get my breath back and calm me down a bit... but that's just me.
I also had previously seen a video of some Chinese provincial badminton competition for children and youth... and it was the strangest thing to see 8-12 yr olds shouting, fist pumping and glaring like Bao Yixin when they win a point...
I suppose this is what they're taught from very young...
To put it super simply; kiai is that scream you hear in most Asian martial arts.
Although many people think kiai means something along the lines of “battle cry” or “spirited shout”, the truth is actually a little bit different.
A quick look at the kanji (Sino-Japanese ideograms) that make up the word should give you a hint as to what the term really means:
Ki = Energy
Ai = Join
In other words, kiai is the convergence of your energy.
Thus, when you scream kiai, you are not only “screaming”, but more importantly compressing and delivering an instant release of your stored energy.
(Of course, there exists debate among people in the martial arts community about the whole “ki/chi/qi” energy thing. Most of those people live on fluffy clouds. Here’s what ki really is.)
When should you use kiai, then?
There are no rules for kiai, but here’s when you could use it:
When you want to channel your energy.
When you need to kickstart your fighing spirit.
When you’re attacking or countering an opponent.
When you do a kata.
When you want to demonstrate your power.
When you need to breathe.
When you want to startle your opponent.
This is not only a martial arts thing, though. This expulsion of air/noise is used by many athletes and is also very much related to breathing exercises in yoga. Many musicians use various breathing techniques to calm the body prior to and during performance to prevent their muscles from stiffening while playing.
The reason for all of these is has to do with gas exchange and the effects on the body.
Hearing some people, it's definitely annoying, but live and let live. As long as it doesn't directly interfere
with your opponent, or openly challenge your opponent, I think it's fine.
By some of the posts in this thread you'd think this was a new phenomena . This is the same discussion as should tennis players grunt so much ...
Some (doubles) players are definitely annoyed by it, so i guess it does interfere ...
And it's just like the opponent at my previous match... I was thinking at my opponent like "Man! You don't have powers do you"... Especially when I lose at the score 19-21.
I don't think the yelling players are oftentimes like Eagles. (No disrespect)... But really even you want to shout but why do it if it distracts other players or making yourself feel powerful.. Then why don't themselves feel powerful like posing confident before the game.
Saina Newal and Carolina Marin does it after each point they score which I think is not to pump themselves up, but rather to put off the opponent. Occasional mini-celebration after a very good point I can accept, but after every point?
There's also that Malaysian XD lady that yells all the time? Can't remember her name but she yells after every point they score then stares out the opponent!