Aaron,
Very good question.
It depends on what type of ?movement?? Are we speaking of everyday, mundane, pedestrian movement, transitions in yoga practice, movement with force and exertion? The rules are different in each case, however can be made simple. Perhaps with a few clues you can answer the question for yourself.
Rule of Thumb: Breathe in the direction of your movement.
Inhale when movement is upward and outward. Exhale when movement is inward and downward. For example, when reaching up overhead, inhale. Exhale when bending over. Inhale again when you stand up. It?s most efficient and reduces internal struggle and loss of energy.
Where is your mind?
When incorporating breathing and movement, you?ll find what?s most important is the breath just prior to that movement: your preparation breath. For example, if you?ve been holding your breath, or if you?ve just exhaled before bending over, you now have no breath to exhale in connection with that movement, and you have to grunt. So movement with breath takes awareness, in this example taking a good inhalation before bending over (with exhalation).
Movement with power can be done either way, depending on the degree of exertion and strain. (Only you can know how much.) For example, when doing a dolphin pushup, you inhale with the exertion and exhale with the release. When pressing a headstand or handstand (when you reach that point), if you inhale as you press up, you release the stabilizing muscles that you would normally rather use. But surprise, that release makes it easier and forces you to focus your energy on a deeper kind of coordination and balance. However, when you?re applying a lot of force, lifting weight, etc., then you want to do it with exhalation so you do hold those stabilizing muscles as a protective mechanism.
My advice?try inhaling with light exertion, as long as it?s not too much, and you will build a stronger, more stabile and balanced musculature. And oh yes, very important to always breathe through your nose whenever possible. Use your mouth to breathe only when volume becomes an issue.
Just one more opinion. Good luck. For God?s sake, don?t hurt yourself.
Siva