According to such as the Gheraṇḍa Saṃhitā,
Aśvinī Mudrā and Mūla Bandha are seen as very
different forms in terms of definition and application.
Regarding application, only Aśvinī Mudrā is focussed around
the repeated contraction of the anal sphincter muscles.
Whereas, Mūla Bandha is a single sustained contraction.
It also appears that there are differing certainties within
the modern use, definition and application of the two terms,
with a single contraction variant of Aśvinī Mudrā often being
passed off in ‘Krishnamacharya’ terminology, as if Mūla Bandha.
For example, Mūla Bandha being described as somethng you
take all the time whether sitting, talking, walking, or eating.
This would not be possible given T Krishnamacharya’s view of
what is Mūla Bandha and its relationship to Uḍḍīyana Bandha.
Comparing Mūla Bandha to Aśvinī Mudrā:
Aśvinī Mudrā can be an outcome of an effective Mūla Bandha.
If Mūla Bandha is good then Aśvinī Mudrā can follow automatically.
But not the other way round, as Aśvinī Mudrā is only
a localised contraction of the anal sphincters.
Also, Mūla Bandha is considered as complete,
whether or not Aśvinī Mudrā is there.
Also, the use of Aśvinī Mudrā can produce gas and
too much use can affect the peristaltic reflex.
Plus avoid in certain conditions such as haemorrhoids.
Āsana can be used for the same effect on these organs.
A direct Aśvinī Mudrā pushes the stomach forward,
so its contraindicated for Mūla Bandha.
Thus, Krishnamacharya’s view of what is Aśvinī Mudrā and what is
Mūla Bandha differed, both in terms of definition, technique, and
application, as well as regarding the student starting prerequisites,
Vinyāsa Krama and links to other layers of their Yoga Sādhana.