In reply to stp:
Good questions, most of which are covered if you read the blog and full article thoroughly, but I will address them specifically below. As a prelude, the primary purpose of the OP was feedback/reference for all the stretching/yoga discussions I have had over the years on UKC, not as a 'how to' guide. Please see a qualified professional who has been educated in 'neurodynamics' and trained in utilising the MLSS before attempting the technique.
> As someone with tight hamstrings I read with interest. Doesn't go into much detail about how to do the Modified Long Sit Slump. Is it simply just doing the stretch in the photos or is there more to it than that?
A full description of the technique (therapist assisted) is detailed in the methodology section of the JSR article. You can access it for free through the hyperlink in the blog.
> According to Russian author Pavel Tsatsouline when we 'stretch' our muscles what we're really doing is resetting our nervous system to allow our limbs to move further.
Yes, overall the evidence for this assertion appears strong, I would argue 'resetting the nervous system' is a more generic a term than sensory modulation of lasting changes in muscle extensibility and stretch tolerance. From a climbing perspective, this relates to what you are trying to stretch, why and when?
> Interesting that neurodynamic tension already takes place with yoga. Though yoga seems like it needs to be practised very regularly and the benefits don't seem to last for 3+ weeks if you don't do anything, unlike the results from this technique.
The current study was of young healthy subjects with tight hamstrings who had not stretched in the preceding 6 months so it's a different sample to those who do yoga 3+ times per week. The study demonstrated a potential 'diminishing returns effect,' that is the more flexible you were at the start of each session the less gain you got from the stretch, although the gains were still significant. That is somewhat consistent with what you are describing but probably requires more research. 'Need' is also quite a strong word, do you have any objective data regarding how often yoga needs to be practised and to maintain what effect?