We are sitting wrong, and our backs know it. "It actually starts with something we were all taught — incorrectly, as it turns out — starting in childhood: sit up straight, shoulders back," says posture expert Esther Gokhale. "What we end up doing is arching our backs by tensing up our muscles -- the ropey ones that the massage therapist will tell you are tight. When we tighten them, we shorten them, and that arches the back, and what that does is it loads the discs [in the lower back] and jams the edges of the vertebrae against each other," she adds. "The key thing is, you want to be upright and relaxed, not upright and tense and not relaxed and slumped." Whether you are lying on the couch, sleeping, or working out, the way you position yourself affects your back. Read more to learn about the techniques you can use to prevent pain in your back -- and to get a link to her TEDx talk, in which she demos what she means.