I am not sure how or why this division came about, but whether or not to bend the knees during a hamstring stretch is a fiercely contested topic in the yoga community. Perhaps it is because injury at the proximal tendon (yellow part of photo below) is quite common among yoga teachers and students. When I lead biomechanics workshops for yoga teachers, I often ask who in the room has experienced, or knows someone who has experienced, proximal hamstring tendon injuries. The show of hands is staggering.
When I first registered for Calculus as an undergrad, it had been several years since I had taken it in high school. For some reason, I avoided taking Math in college, but then ended up choosing it as my minor (my major was Women’s Studies). Anyway, on the first day, the professor started lecturing, writing what he was saying on the blackboard. When he finally paused, I looked up and saw that he had written simple line of symbols but I had composed an extensive paragraph written in actual words. I had to relearn the alphabet of mathematical symbols if I was going to succeed in this class.