Maybe i need to give it another go but I couldn't finish this book; found it tiresome due to all the "personal anecdotes/narratives" forming the backdrop for the book. It could also be that i am somewhat well-read on this subject due to my interest in traditional Yoga/Pranayama/Martial Arts and hence felt underwhelmed. What i had hoped to find in the book was a catalog of techniques (based on tradition or modern) from "Western Scientific Research" showing actual measurable results in terms of Human physiological parameters. But whatever was mentioned was never clearly explained with actionable steps. However the webpage for the book's bibliography is a treasure trove of pointers to papers and reading for further research.
Since you are also interested in the same subjects as me, do you have any other specific suggestions for what i am looking for?
Ah, I can completely see why you would find it frustrating—I enjoyed the anecdotes and it made for very light holiday reading, but then it was indeed light on detail.
If you go to the end of the book, just before the Notes section there is a short chapter which lays out the basics of most of the breathing techniques. I've found that to be enough to experiment a little and while brief it's enough as a starting point.
Sadly I don't have any recommendations for breathing techniques outside of those espoused by Wim Hof, which are based in part on Tummo.
Given that this book (Breath) has been published and the recent increase in popularity the topic is seeing I am hopeful that we will see some follow-on works (if they don't exist already) that will break these techniques down in more detail. As it stands it feels necessary to piece together elements from different books to get a more complete picture regarding how these techniques work and what is possible. I would certainly be interested to see a collation of results seen in athletes.
Since you are also interested in the same subjects as me, do you have any other specific suggestions for what i am looking for?