We had a discussion about air during yesterday's Renaissance consort meeting. A new person to the group, a professional oboe player in civilian life, mentioned that she felt out of breath playing the alto recorder, to which two members replied that their shawm teacher tells them not to "blow," but rather to "exhale" through the instrument.
My thoughts waited a day or so before they collected themselves, so I'll share my observations here.
When I play the recorder or the flute I think about using the tongue to move the air through the instrument and out into the world. Exhaling is too passive for me, and blowing without using the tongue to move the airstream feels like a waste of air. I find that exhaling by itself lacks purpose and direction, because it doesn't take the all-important tongue into consideration. I always use the tongue to push the air, and then I use it to move the air stream through the instrument. A certain amount of "blowing" does happen, but it only happens once the air column has been set into motion.
When I play viola or violin I begin my bow stroke with a combination of right-hand fingers and wrist. I find that they function together much like a tongue functions when playing the flute or the recorder. Then I use a combination of my fingers, hand, wrist, arm, and shoulder to move the bow and regulate its speed and pressure. The movement starts (or keeps) the string vibrating, which in turn sets the wood and the air inside the instrument into motion. When I move the bow, I push or pull the air (up bow is the same as push and down bow is the same as pull) out of the instrument. It's nothing like blowing, though once the bow is in motion, it feels a little like exhaling. It particularly feels like exhaling when I actually exhale while moving the bow.
We inhale and exhale while playing a stringed instrument (because we can, and because we have to in order to live). It feels both life-enhancing and music-enhancing. The act of inhaling and exhaling when playing strings does not make sound or prepare to make sound. What happens inside the body (what you cannot see) has little bearing on the way notes are produced. When playing a wind instrument the outside of the body (the part that you can see) remains relatively still. Physical movement (aside from the fingers, the breathing mechanism, and the occasional combination of lip and cheek) is superfluous; it does nothing to improve sound quality or musical expression.