Attacks are done with the lungs almost empty.
Always keep at least 10% percent of your breath at all times, don't let the last bit go. You need this remaining air so that your body can continue to function.
Before initiating a move exhale 90% of your air then retain the breath during the move.
A kiai will use 10% of your breath therefore, if the move is going to be preceded by a kiai exhale 80% of the breath, kiai and then execute the move (10% of the vial capacity remains during the move).
The Japanese word for breath or breathing is ibuki. Soft internal breathing is in ibuki. Hard internal breathing is yō ibuki.
Based what I have learned at the dojo and this article in Black Belt Magazine (1966), The Cat, I believe this philosophy of breathing comes primarily from Grand Master Shimabuku's Gojo Ryu lineage. Quoting the article...
There is another form of kata for which the school is famous and without which no explanation of the Goju style would be complete. That is the school's breathing kata. No one who has ever witnessed a Goju man practicing his breathing kata under a full head of steam will ever forget the experience. It is an awesome and, to those of a more timid turn, sometimes frightening experience. A good Goju man can be heard half a block away and more while engaged in breathing exercises.There are two types of breathing practiced, the in-ibuki and the yo-ibuki. The in-ibuki is the soft but firm type of breathing which starts from deep within the abdomen. This is similar to the type of breathing which is practiced in Yoga and Zen meditation, and is usually directed towards spiritual and meditative matters when practiced. Goju adherents never tire of repeating that this is the normal way a baby breathes. It is only when we get older that we learn to breathe from our chest.
The yo-ibuki is the hard style of breathing. The sound effects are menacing. The breathing is loud and heavy and comes from deep within, producing something of the sound of a full-throated lion about to strike. The inhaling is done in quick intakes through the nose while the exhaling is a prolonged process of short breaths through the mouth. In exhaling the whole body is tensed, including the throat and esophagus. This tightens the air passage and the air is forced from the abdomen. This whole process is said to be combative or animal-like breathing.
The tensing that is carried out during the breathing exercises is similar to that carried on in dynamic tension and isometric exercises. Tensing is believed to build up physical strength. And that goes internally, too, where the breathing is said to strengthen the heart and other vital organs. The student is taught never to exhale all his breath at once but to ration it out in short breaths. One reason is to always save a little breath so that an opponent cannot strike when one is out of breath and at one's weakest just before inhaling. The idea is always to save a little breath to counter. A good Goju man who is really warmed up will stride across the floor rippling every muscle from head to foot while engaged in powerful animal-like breathing. The effect can be quite spectacular.
But there is another side to the breathing exercises, the side concerned with the mental and spiritual aspects of karate. By its very nature, this is the side most difficult to grasp for many persons, especially Westerners. The most advanced type of breathing exercise is that in which all of one's strength is concentrated on a specific feeling or thought. It is through concentration and meditation that man learns to improve himself.
