Low back pain can be a tricky symptom to assess; thankfully more often than not, the discomfort can be attributed to soft tissue tension and weakness, frequently traced to the deep and mysterious QL, or, quadratus lumborum. The QL is our deepest abdominal muscle, though easy to consider a back muscle due to its location and function. It is located under our superficial back muscles posteriorly, and under our superficial abdominal muscles and psoas anteriorly, where we bend at the waist.