Breathing is one of those things that is just there. Or, is it? Do you always remember to breathe when you’re practising yoga?
It seems to amuse my yoga students when I ask them to breathe – not because I’m trying to be funny but because they recognise it’s so easy to suppress breathing ‘when push comes to shove’. In the effort of attaining a challenging pose, relaxed breathing gets jettisoned.
There are many theories of how to breathe for best results when doing asanas or pranayama. I’ve been in Ashtanga Vinyasa classes where some students sound like Darth Vader, in the way they do ujjayi (audible) breathing. In other styles of yoga, you are told to just breathe naturally…if we could only figure out how that’s done.
The most meaningful pranayama sessions I’ve done have been when I do no more than observe my breath. And, we all know how hard it is to be a non-meddling witness to anything, let alone something as subtle as breathing.
Chip Hartranft, in The Yoga Sutra of Patanjali,* has written about the distinction between regulating the breath and simply observing it. He says:

…steady observation alone is enough to bring about unforced changes in the breath’s shape and texture. Indeed, no form of conscious, deliberate effort can make the breath as soft and unhurried as it becomes spontaneously through sustained mindfulness. And as respiration grows inconceivably spacious and subtle, it ceases to be a suitable environment for agitated mental states.
Bahya-abhyantara-stambha-vrttir-desa-kala-samkhyabhih paridrsto dirgha-suksmah

As the movement patterns of each breath – inhalation, exhalation, lull – are observed as to duration, number, and area of focus, breath becomes spacious and subtle.*