From Yoga Sūtra Chapter Two verse 47
Krishnamacharya taught that the
common denominator for successfully uniting
both aspects of relaxation and the infinite
within the practice of Āsana is the breath.
He saw it as continued effort
and synonymous with giving life.
The continued effort of the breath is that which gives life.
– Paul Harvey on Yoga Sūtra Chapter Two verse 47

Paul’s Yoga Mālā – A Thread of Pearls from Patañjali’s Yoga Sūtra