Mantra, kundalini and hatha yoga all stress breath control as a key trick in energy input regulation (pranamaya). They view the solar plexus as a storage cell for prana. Pranamaya claims it can get beyond the antinomies of pure reason by diddling the nerves, so there is much emphasis on raising the kundalini ie. constructive tripping. In any event, you aim to increase your lung capacity, with more oxygen and better mileage. You breathe deeply enough to distend both chest and abdomen, then you try to squeeze out every particle of the used air.
The ratio of inhalation : retention : exhalation times is 1 : 4 : 2. You want to get the actual numbers as high as possible, at least 8-32-16 seconds. That's 16, not 1.
You will have noticed that one of your nostrils is always a little more open than the other. They take turns being the more open one. Yoga sets out to keep the changing of the guard as regular as possible on the theory that prolonged domination by either nostril means impending disease.
So you spend n seconds breathing in through one nostril, then hold the breath 4n, then spend 2n exhaling through the other nostril. Repeat the other way round. That is a complete cycle. You do ten morning, ten evening until 8-32-16 or better is routine. If you want to be culturally sound you use your right hand, closing your right nostril with the thumb and your left with the ring and little fingers, not the placket finger.
In abdominal breathing (kapalabathi) you use distention of the abdominal muscles alone to suck in the air slowly, then sudden sharp abdominal contraction alone to force it out fast. Do 3 x 15 reps before each session of pranamaya. Best in lotus position as you can lock when you start to dissolve: while holding the breath, lock your chin as far as possible into your jugular notch and lock your rear end too while pressing your left heel into your perineum. Practice hardening the pressure by locking your stomach up into your diaphragm for a triple lock. Unlock just before exhalation.
There are various advanced combinations of nostrils and locks once you get this all down. Severely contracting and distending the stomach are also minor exercises in their own right. You can go a step beyond kapalabathi and do sharp exhalations squeezing the whole respiratory system. See if you can carefully get to the point where you feel you can hyperventilate on and on without passing out.
