Does passive hip stiffness or range of motion correlate with spinal curvature and posture during quiet standing?

It has been postulated that hip muscle stiffness can be inferred from postural assessment, and that predictable relationships exist between passive stiffness of opposing muscles. Despite a lack of evidence to demonstrate such relationships, manual therapy textbooks continue to direct clinicians to treat hip muscles following postural analysis.

Do significant correlations exist between standing posture, and hip muscle stiffness and range of motion?

20 participants volunteered for this observational study. Passive hip stiffness was calculated as the derivative of the moment-angle curve measured during leg raising in a variety of lying postures. Stiffness was measured during hip flexion, extension, abduction and adduction. Stiffness data was obtained during the first degree and at ROM, and at the highest common angle achieved by participants in each posture Spinal curvature and other postural components were measured using a motion tracking device. Spearman rank coefficients were determined to assess any correlations between passive stiffness, range of motion, spinal curvature and other postural components.

Consistent relationships were found between maximum range of motion and hip stiffness at the common angles (P < 0.01), but not at maximum stiffness (P > 0.05). Consistent correlations were found between abductor stiffness and Q-angle (P < 0.05). Hip extensor range of motion correlated with lumbar lordosis (r = -0.472, P = 0.036). Other correlations were reported, but typically lacked consistency between left and right sides. Spinal curvature did not correlate with hip stiffness in frontal or sagittal planes (P > 0.05).

Significant correlations were few compared with where correlations lacked statistical significance. This study demonstrates that overly simplistic assumptions about spinal posture and hip stiffness cannot be supported. Hip muscle stiffness should only be targeted in treatments where testing has demonstrated a direct need, and not assumed based upon postural assessment alone.