Reliability of COP Measures in Healthy and Low Back Pain Subjects During a Dynamic Task

Study design. A test–retest design. Objectives: To study the reliability of the postural stability measures during whole body dynamic conditions in healthy and low back pain (LBP) subjects. Summary of Background Data: Postural control is an essential prerequisite for dynamic motions such as lifting, lowering, and repetitive trunk bending tasks. Test retest reliability of center of pressure (COP) measures is well documented in static conditions but such results may not be applicable to dynamic conditions. To the authors knowledge this has not been investigated in dynamic conditions. Methods: Twenty four subjects (12 healthy and 12 LBP) performed repeated trunk bending in two different conditions of high and low speed in sagittal plane. All measurements were repeated and recorded with an interval of 7-10 days later. COP data were used to calculate standard deviation of amplitude, standard deviation of velocity in anterior-posterior and medial-lateral directions, mean total velocity and path length. Relative reliability was assessed using intra class correlation coefficient (ICC) and absolute reliability using standard error of measurement (SEM), minimum detectable change (MMDC) and coefficient of variation (CV). Results: Results in both groups revealed that mean total velocity and standard deviation of amplitude in anteriorposterior direction have an acceptable good to an excellent reliability with ICC range of 0.61-0.89. In healthy group the rest of others parameters also demonstrated an acceptable good to excellent reliability (range 0.6-0.97). In LBP subjects, in addition to standard deviation of amplitude in anterior posterior direction and mean total velocity, standard deviation of velocity in A-P in high pace condition also showed good reliability (ICC=0.69). Conclusion: Mean total velocity and standard deviation of amplitude in anterior-posterior direction are suggested as a good reliable parameter to use for evaluation postural stability in dynamic situations such as lifting and complex trunk movement