I've read online (probably from these two sources Athlean-X and Mike) that when one has a tight muscle that the antagonistic muscle tightens up as a defense mechanism. What I am trying to understand is why the body does this. From my intuition it seems that tightening up just makes the tight muscle vulnerable to wanting to stretch it and snap it, so I can't imagine how tightening is a good idea biologically. Furthermore, even if I choose not to stretch it (which is the instinct) it doesn't inform me what the real issue is nor does it seem as a way to defend anything. Thus, how is tightening up defending anything? How does this (perhaps from an evolutionary perspective) make sense? Why does this happen?