Most of us think that stretching means that you just literally stretch the tissue
, the muscle itself, and that's it. Well, that's not really true. What is actually happening is that you are increasing your tolerance to it
and the nervous system is actually the one allowing you to perform those positions.
Stretching sensation is more an issue of sensation, not mechanics.
Think about it: What happens when you go over your range of motion - you feel either pain or your muscle stiffens. Both of those are protective mechanisms of your nervous system.
The priority of your CNS is to keep you alive at all costs. You might want to run a marathon, climb a mountain or get into hanumasana (splits), but your CNS doesn't care about that. It only wants to protect you from physical threats. The CNS's beliefs about what is a danger to survival are based on millions of years of evolution - eaten by predators was a danger. Therefore, injuries like a pulled muscle can kill you. And the most obvious protective mechanisms are pain and the startle reflex, but also weakness and stiffness.