Yoga Sutra 2.50 Systematic long and subtle breathing
Observe your breath according to location, duration and count.
What is the duration of your natural, involuntary inhalation?
How does it compare to the duration of your natural exhalation?
Is there a brief pause during the transitions between exhalation and inhalation?
Can you direct your breath to move the lower torso, mid torso and upper torso?