Yoga Sūtra Chapter Two verse 47

प्रयत्नशैथिल्यानन्तसमापत्तिभ्याम् ॥४७॥

prayatna-śaithilya-ananta-samāpattibhyām ||47||

Both relaxation of continued effort and unity in the infinite.

prayatna - continued effortśaithilya - relaxationananta - endless, boundless, eternal, infinite; the first serpentsamāpatti - coming together, unity

Commentaries and Reflections

T Krishnamacharya:

The practice of Āsana without breathing and without remembering Ananta has no value.

TKV Desikachar:

The test for intelligent effort is the response of the breath.

Paul Harvey:

When working with the Breath in Āsana its perhaps less appealing initially,
but ultimately more attractive, satisfactory and effective,
to integrate  a focus of Samāpatti (Unity) of
Śaithilya (Relaxation) in Ananta (the Infinite),
through a developmental Sādhana (Means to Accomplish)
on the Siddhi (accomplishment) of Dīrgha or Length,
supported by Sūkṣma or Subtlety.

From Yoga Sūtra Chapter Two verse 47 T Krishnamacharya taught that:
– the common denominator for successfully uniting (Samāpatti)
both (Bhyām) aspects of relaxation (Śaithilya) and the infinite (Ananta)
within the practice of Āsana is the Breath.
He saw it as Prayatna (continued effort)
and synonymous with Jīvana (giving life).
The continued effort of the Breath is that which gives life.

Two primary roles in the adaptation of Āsana
to the needs and potential of the student are
Facilitating a decrease of tension within the body
Facilitating an increase of attention within the breath.

Our continued efforts with the Breath in Āsana
is that which helps enliven our various levels of interaction with
our inner and outer worlds as expressed through the Pañca Maya.