long story short: I'm a yoga teacher who is very interested in optimizing body performance and health of tissues both for myself and my students.
I have been practicing the foundation protocols since October 2014 and have also signed up for the Handstand and Stretching courses and really enjoying these (and so have the yoga students I have shared some of the basic exercises with in class).
I wanted to post links to a blog written by Jules Mitchell, a yogini who is doing her Master's Thesis on the biomechanics and science of stretching. She has some pretty amazing insight into how the body works (much of it contradicts a lot of what is present in common knowledge about flexibility, including the yoga world). In fact, the only program in which I have found some of the principles she is researching to be applied thoroughly is in the Gymnastics bodies' stretch program, which had me excited when I started because this program seems to have been generated through the years, likely a product of much trial and error and effectiveness in function.
here is one of her most relevant posts to the subject:
http://www.julesmitchell.com/stretching-and-muscle-control/
A highlight of the post is that one of the main determinants for increased ROM is stretching tolerance (i.e. nervous system 'allows' it), rather than muscles that have become longer through stretching. She does a better job at explaining it than I could so I'll let you check out the link!
Happy training
photo from Bukh 1925