Flexibility improvements in the first three weeks of stretching are largely due to neural adaptations and increased stretch tolerance.

“how acute bouts of short-term stretching up to three weeks can improve stretch tolerance. I think that's a key point that in the short-term, the first three weeks of embarking on a stretching and flexibility program, much of the improvements come from the short-term neural improvements that we talked about before of inhibiting the spindle reflex and so on. And also, a stretch tolerance, a comfort with doing the movements and maybe even a comfort in overriding some of the pain mechanisms.”