question: Recently I have been having a pulling sensation down the back of my thighs (left much more than right) that radiates down behind my knee. It feels as if I am stretching, but I am not. It is not constant but often hurts when I walk/run. I have also found that if I stand and bend back at the waist (like the very beginning of a backbend) the pulling is really bad. Does this sound like something I need to have checked out?