Actions of the quadratus lumborum

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The quadratus lumborum acts differently depending on whether it contracts on one side or both. Unilaterally, it pulls the pelvis up on the same side and bends the trunk laterally toward that side, and it can help rotate the lumbar spine toward the same side as well. This same-side hip hiking is a key way it contributes to gait and pelvis stabilization. Bilaterally, the muscle helps straighten the lumbar spine and provides a stable anchor for the 12th rib during breathing. So, the pattern described—lateral flexion of the trunk to the same side, possible ipsilateral rotation, and hip elevation on the same side, plus bilateral spinal extension and rib stabilization—best captures the actions of the quadratus lumborum.