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.
4.Continuity – Continue to breathe without interruption unless there is a specific training purpose that requires you to hold your breath.
5.Pendulum – Allow the breath to natural swing from inhale to exhale without interruption of force (the breath will pause briefly after inhalation and exhalation.)
Holding the breath creates extraneous muscular tension, so to avoid adding stress to the body it is important to breath continuously without force. You often hold your breath without knowing it, but you can easily become more aware of breath interruptions by analyzing yourself periodically throughout the day. You can also familiarize yourself with the moments in your day when breathing stops. Once you are familiar with your habits, you may start to predict problem areas and breath consciously during those times until it becomes a natural habit. Therefore, practice in class and out of class.
It is common to hold the breath getting in/out of the car, during fast paced work, doing something that requires precision, under stress, when lifting objects, squatting, or even thinking analytically. Every individual is unique, but you may notice interruptions during these and other moments.