Uddiyana Bandha is often misunderstood as a simple contraction. By perceiving the updraft of the iliopsoas as a simple contraction, practitioners mistakenly tighten their gut. But Uddiyana Bandha involves the length (and width) of the entire iliolumbar region. This became clear to me in my study of Iyengar Yoga. Some time ago. B. K. S. Iyengar made the point that the essential movement of Uddiyana Bandha is accomplished in Urdhva Dhanurasana (Upward Bow Pose). In this backbend, the iliopsoas muscles and anterior lumbar spine are not contracted but fully lengthened. Iyengar’s point was that the length of the abdominal spine and adjoining psoas muscles is instrumental to the performance of the bandha.