As has already been mentioned, it's best to inhale through your nose and exhale through your mouth. You will be able to exert harder if you exhale while exerting .. for example, if you notice someone benching some heavy weight, they'll always puff out hard while pushing up.. this helps your body create more pressure. Imagine trying to push something while inhaling in.. would take away from the pushing wouldn't it? So basically, exhale when you strike or exert your strength hard in any way.
Also, the hissing sound you probably heard is guys exhaling through clenched teeth. This is for good defense.. you can take a much harder blow to the jaw without getting KOd if it is clenched and tight than if it is slack. It hardly takes any power to KO a guy with his jaw hanging loose, because the sideways snapping of the jaw or the neck is what pulls on the "lights out" nerve that connects to the brain.
Last edited by Liddellianenko; 01-22-2008 at 11:29 AM.