During a dynamic movement assessment, a client demonstrates hip hiking during a basic gait pattern. What specific muscular inefficiency in the frontal plane of the lower body is most directly indicated by this observation?

Hip hiking during a basic gait pattern refers to the excessive elevation of the pelvis on the non-weight-bearing side, which is known as the swing leg side, during its swing phase. This movement occurs in the frontal plane, an imaginary plane that divides the body into front and back halves and allows for side-to-side motions. The specific muscular inefficiency in the frontal plane of the lower body most directly indicated by this observation is the overactivity of the ipsilateral quadratus lumborum muscle. The quadratus lumborum is a deep muscle located in the lower back, connecting the iliac crest (part of the pelvis) to the twelfth rib and lumbar vertebrae. Its primary action in this context is to elevate the pelvis. Its overactivity is considered a muscular inefficiency because it is a compensatory strategy. This compensation is typically employed to help clear the swing leg from the ground when there is insufficient movement at the hip or knee (insufficient hip or knee flexion) or at the ankle (insufficient ankle dorsiflexion) on the same leg. Rather than the limb itself adequately flexing to clear the ground, the entire pelvis is raised by the overworking quadratus lumborum to achieve necessary ground clearance.