Watching Gina Carano work out on the punching bag, i noticed she seemed to be exhaling each time she hit the bag. She was making a hissing sound. Is the purpose of that to deliver more oxygen to the muscles or something else?
it tightens your abdominal musculature, which in turns helps apply more force with your entire body. it's something you should know pretty much from day 1 in any martial art.
The hissing tends to suggest people are constricting their breathing by pushing their tongue up. That's a mistake IMO, you should be breathing as freely as possible. Where any noise should come from is from having your jaw closed, rather than pretending you're a snake Mitch
Lots of theories on this one. The karateka's totally go hardcore on this to some extent as do many of the CMA's. There is a growling sound associated with most Muay Thai that is the result of the same thing. Overall I don't think it's detrimental unless you are pushing to the point that you are getting caught with your jaw wide open... bad to take a shot like that for sure. Many boxers do the whole exhale on punch connect thing as well. Some do it... some dont. Many different styles have conditioning drills the involve big deep exhales. Daito-ryu has several that can be very difficult to the uninitiated.
I find the most useful thing about it is that it stops me from gassing for a while, as my breathing pattern is fairly stable. Also, if someone punches me, there's no air in me to get winded by.
This is the big one. When you inhale your Thoracic diaphragm contracts thereby reducing intra-thoracic pressure. Not a good state to catch a shot in. Easy to get creased like that. When you employ the abdominals and the intracostal muscles to forcefully exhale you are increasing intra-thorasic pressure. A much better state to catch a shot to the belly in. Not a guarantee that you won't get sat down.... or double over... but it helps your chances. A simple test you can do... lay flat on your back... and try each of the following: A) your partner stands above you with a 9kg medicine ball... you inhale hold it (brace) and then have him drop the medicine ball from shoulder height directly onto your belly... B) your partner stands above you with a 9kg medicine ball... you exhale forcefully, immediately have him drop the medicine ball from shoulder height directly onto your belly... It won't take much science to figure out which one is a more desirable state to wear a shot in.
I generally find it helps me to remember to breath. Many times, particularly on bags rather than sparring, I'm slugging away and gas, then realise I've not breathed for a few seconds. Big problem! So if I make a funny noise or force the breath each strike, it helps keep up my breathing rhythm.