I'm always interested in 'the science' of Yoga.
Yogani said:
[holding breath] places a slight challenge on the
oxygen supply in the body. This is what draws prana up into the
nervous system from its huge storehouse in the pelvic region
Interestingly, to me anyway, this may be another example of exploitation, in Yoga, of a hormetic mechanism -- that is, the positive exploitation of the body's corrective counter-reaction to a normally 'negative' condition. In exploiting hormesis, we deliberately establish a mild 'negative' condition with the intention of obtaining the body's 'positive' counter-reaction to it.
I've noticed that exploitation of hormesis seems to pop up again and again in Yoga.
In my mind, possibility of a hormetic mechanism stand out in three things in particular which I have found so far --
1. Amaroli, where we suddenly increase the concentration of the body's own chemical toxins, to positive overall effect;
2. Hatha Yoga Asanas: stretching of muscles in asana, which subjects them to a mild and broadly-distributed physical trauma and forces a response from the body of broadly-distributed healing activity;
3. and Kumbhak -- exploitation of a temporary, mild, oxygen deficit.
There's room for a good yoga/science essay some time, called 'Yoga and Hormesis'.
By the way, acupuncture may be another exploitation of 'hormesis'.
(should this be in Yoga, Science and Philosophy? Well, it seems to fit both forums... I chose what I thought was best.)