The most important stretch in my Stretch Away Muscle Pain system is the Lunge stretch.This stretch targets the psoas muscle, which is responsible for most low back problems and effects every major joint in our body. When the psoas muscle gets too tight, it tilts our pelvis forward, causing poor posture and our trunk to be forward. This makes muscles have to contract and puts marked stress on our back and other areas.It is the most important stretch of the Stretch Away Muscle Pain Stretching System.