As “yoga” and “stretching” are often used synonymously, let’s consider what’s happening in a yoga asana* beyond tissue lengthening, i.e. stretching.

On the off chance that my stick figure yogi isn’t going to get me into the Smithsonian: this practitioner is in a forward fold, their legs on the right and head/arms to the left.

💧 COMPRESSION: as one tissue group lengthens, there’s a corresponding compression, usually on the opposite side of the lengthening. We could call the main recipient of this compression the “fluid body” (taking this from Tias Little): this includes blood, lymph, the gooey morass of interstitial fluids, and the organs and glands.

And while of course it’s not just the fluids that are being compressed, the map of the endocrine system — which uses the blood as its “highways” to transport data between glands — is a good one to consider the benefits of compression.

✨ AWARENESS: two pretty distinct aspects here:

1. Data going from the limbs to the CNS = afferent nerve signals = “I can feel [whatever you’re feeling]” = proprioception and interoception (which are processed in distinct areas of the brain, but we’ll lump them together here as “sensory information coming into the brain”).
2. Data going from the CNS out to the limbs = efferent nerve signals = “I am moving/stabilizing [whatever you’re moving/stabilizing]” = motor control.

Side discussion: awareness is a big word. Does it extend beyond the nervous system? I sure think so. But we immediately run into “the hard problem” of consciousness: how does one study the thing that is doing the studying? We avoid that here by talking about what qualities of the nervous system we do know, which involve relaying information via neural impulses.

↔️ STRETCHING: much of what makes the distinction in the quality of a pose is the apex of the stretch. Whether you have a rounded back or not, your whole back body — or the superficial back line, to use the language of the Anatomy Trains — is stretching.

So what makes a good forward fold vs a bad one (and please, all arguments about everyone getting to do their own thing notwithstanding; of course that’s true; but some movements are more well done than others)?

The answer is a question: where are the apex(es) of the movement? In a forward fold, like this as in many asana, it’s the hips folding into flexion, aka hinging at the hips.

GERM LAYERS OF THE EMBRYO are also part of this schematic**

There are three that make it all the way through (sorry, neural crest). The guts 💧 arise of the endoderm; the nervous system ✨ and skin are of the ectoderm; the fascia, bones and musculature are of the middle, and quite pervasive, layer of the sandwich, the mesoderm.

* yoga asana, or any stretching whilst paying attention for that matter, actually any movement at all; yoga is just easier to study because its movement stops now and then

** want to go even further out on a limb with me? If you know the Ayurvedic doshas …

💧 endoderm = kapha

✨ ectoderm = vata

🔥 mesoderm = pitta

Hope this was useful for you