The following is an excerpt from the 7 principles of Russian Breathing according to Vladimir Vasiliev with commentary by Systema SLC. For more information pick up Let Every Breath: the Secrets of the Russian Breath Masters.
3. Sufficiency – Only inhale or exhale as much as the action requires (never inhale to full extent or exhale to full extent.)
Another word for inhaling more than required is hyperventilation. Hyperventilation may take form as a gasp for breath or quick inhalations without equal exhalation or, for those who are sensitive enough, tension in the chest, neck, and face. It less common to exhale more than necessary, but over time over-exhalation may starve the body of oxygen or create excess tension as well.
To avoid hyperventilation and learn to use breath effectively, never gasp for breath before or after holding the breath; if you feel you are ready to gasp for air, burst breathe with short inhales and exhales (your abdomen should expand on the short exhale as if you are coughing.)
If you are at rest and your heart is beating in normal cadence, there is no need for quick or heavy breathing. Inhale through the nose and exhale through the nose in a comfortable and natural fashion. When you begin to work (bending over, squatting, standing up, moving briskly) inhale through the nose and out the mouth. As work amps up, (running, stress, rolling, fear, falling,) you may speed up breathing to match the intensity of your work.
Never wait to recover until it is needed badly, because it may take longer than you’d expect to come back to resting state. Always keep your breath in mind, match breathing intensity with work intensity and recover as often as needed. If you find yourself recovering too often, perhaps you are not breathing efficiently, or recovering completely.
This principle applies to all Systema work. Sufficiency in movement, action, reaction, effort. . .etc.