I thank you for your blog posting and your interest in this aspect of the practice as it’s helped me articulate more of my own ideas.
I am curious to know in what sense is the primary series “nearly impossible” for some students to master without “daily adjustments”? On what are you basing this observation? Also, on what are you basing the supposition that “without regular assistance, students would make little or no progress”? I’m remarking on this because your statements aren't borne out by my experience, both practicing and teaching ashtanga vinyasa. For what length of time have you observed a body of students, i.e. one year, three years, five years?
The primary series is a progressive sequence, as you’ve noted --- over time, the later poses make the poses that precede them easier. But it’s important not to forget that the earlier poses make the later poses possible.
In a larger sense, on the anna maya kosha or purely physical level, the intermediate series begins to seriously work with the plexus of nerves that runs through the sacrum; to use another, more yogic map, on the prana maya kosha level, and perhaps deeper, nadi shodhana begins to work on the kanda, the egg-shaped “knot” where the three main nadis join, and on the sushumna nadi, which extends from the muladhara to the crown of the head.
Do these channels feel familiar? They should, as intermediate goes to work on them hammers-and-tongs with an increasingly and progressive series of intense backbends, and then heading in the opposite direction with a series of intense forward bends. The advanced sequences of ashtanga then flip-flop between these extreme directions with, shall we say, less compassionate sequencing.
To further elaborate on your ideas about intermediate and to add some clarity, pasasana is the beginning of preparation for backbending. Its twisting aspect continues the alleviation of forward bending that began with setu bandasana, and it begins to strengthen and open the hip flexors and calves, as well as strengthen the soleus. These aspects are integral to kapotasana and urdvha dhanurasana.
Krouncasana will continue to lengthen the quadriceps, hip flexors and psoas, as well as the IT band on the extended leg; again, all of which are important for backbending. We are lengthening the connective tissue in the legs and in the front core of the body.
Supta vajrasana then becomes a counter-pose to kapotasana and helps reset the sacrum. Bakasana, with its rounded spine, continues the transition into backbending counterposes. Chief among its aims is to strengthen the abdominal area, which when contracted will help lengthen and elongate the muscles of the back.
Karandavasana, and to a certain extent tittibasana, are gentle counterposes to dwi pada sirsasana, as the spine is gradually brought out of the state of extreme flexion and the core is once again engaged and strengthened to help return the spine and the muscles of the back to a sense of neutrality. Karandavasana also involves an intense rounding of the spine in order to fit the shins into the armpits. (Mayurasana then becomes the counterpose for the wrists, forearms and spine, which bows upward from the base of the elbows.)
While it may be more challenging to do eka pada sirsasana than dwi pada sirsasana, the risk for injury in dwi pada is much, much greater, which is generally why it is given after some proficiency is demonstrated in eka pada sirsasana. Yogi nidrasana is aptly named, too --- it’s a relaxing, resting pose, and it begins the transition away from leg-behind-head, which carries through into tittibasana.
I’ve found it helpful to expand my ideas of asana sequencing beyond the pose/counterpose dialectic and into a triadic approach. We begin with the attack, or the ascension, the rising note, or the Brahma/creator aspect of the trimurti, which evolves into the sustain, the plateau, or the Vishnu/preserver aspect. This is followed by the decay, the decline, the Shiva-destroyer.
Baradvajasana begins the Brahma aspect of the leg-behind-head sequence, culminating in dwi pada sirsasana, which may be considered the Vishnu of the sequence. Yogi nidrasana begins the Shiva aspects of leg-behind-head.
These asanas are also nested as pieces of different triadic series for backbending, twisting, and strengthening.
I’m not a regular follower of your blog, so I can’t comment on recurring themes in it, but I do get a sense that you’re focusing on a lot of the minutiae of the asanas --- hands must be bound, heels must be grabbed, et cetera, et cetera. This can be helpful, although to borrow a phrase from Matthew Sweeney's Ashtanga Yoga As It Is, it’s a phase through which one ought to move.
I practice with a woman who once told me, “I used to be concerned about taking my heels. Now I just make the shapes.” This is after more than 10 years of daily, dedicated practice; I think it’s important to note that in order to move beyond a state of being concerned about “grabbing her heels,” she had to first experience that state.
Part of the “nadi shodhana,” regardless of being able to grab your heels or lick your coccyx, is to “make the shape,” even if the shape is a fairly intense back- or forward bend, while at the same time cultivating a dispassionate, ease-full, skilled state of observation and awareness. This state can be measured by a yogini’s fluid entry and exit from the pose, her stability and calm (Patanjali’s famous “sthira sukkham”), and of course, the quality of her breath, both the out and in-breath. Which is ideally even, measured, and calm (Again, according to our friend Patanjali, “dirgha” and “sukshma”).
My speculation on part of the reasoning behind the way poses are given in Mysore is that Sharath can see a student’s avoidance of a pose, and for the most part he’s very practiced in reading a student’s body and listening for the student’s breath to determine their sthira and sukkham while they’re in a pose.
This cultivation of calm, dispassionate observation in a pose as stimulating as kapotasana --- which ignites the body’s parasympathetic nervous system --- necessitates and is predicated on a retraining of the nervous system. This development of an internal candle flame that is unwavering is what I take “nadi shodhana” to mean.
It can take years to master an intricate physical and mental skill that requires both strength and flexibility. I’ve read that it takes seven years on average to “master” a skill, that is, to be proficient and skillful in its use. In that context, one would expect at least three to five years developing journeyman status.
So as I mentioned before, it’s not as important that, for example, one has to be lifted back up from karandavasana --- though most everyone, given time and practice, can learn to place their feet in lotus and lower to their arms --- it’s the ease, fluidity, and most importantly, sense of dispassionate observation that’s important. This is in itself a skill to be refined, learned and polished like a fine jewel.
I can think of many reasons why someone ought not to proceed through primary without at least “making the shape,” and chief among those is injury. There is also a tendency to gloss over and ignore those poses we do not like or those we find difficult. As the sequences are progressive, when you skip something now, you pay for it later.
To return to intermediate sequencing, bhekasana is very important to kapotasana, as is laguvajrasana, among others ... until these two are not only comfortable but done correctly, kapotasana is very, very difficult. This is part of the reason why these backbends should generally not be given as a chunk or “subsequence.” In fact, in my experience, kapotasana is incredibly difficult, indeed impossible, unless and until one can slowly and calmly lift and lower from standing into urdvha dhanurasana.
Ultimately, I must ask you how many of your ideas about the practice are related to your own desire to get the next pose? As Sweeney notes, again from Ashtanga Yoga As It Is, and I can second through my own practice, this is a difficult phase of the practice, but one that I believe many people, if not all, go through, and one that is allayed through continuous, steady practice through all stages and phases of life --- including injury, illness, and massive life-shifts.
The triadic view of the sequencing is helpful, and I also find a general triadic view of my practice in general as helpful. One might, for example, go through a Shiva phase of practice when one has to be on-site at the construction yard at 7 a.m., which leaves an hour of practice time at 5 a.m. only three days a week. The desire to feed one’s needs for the next pose abates significantly in the face of life’s ebb and flow.
Again, I thank you for the stimulation your post has provided. I hope you derive a nugget of value from this that may reflect on your own practice, as your post inspired me reflect on my own practice.