Test- retest reliability of coordination and movement pattern stability measures during repetitive trunk bending in healthy and non specific low back pain groups

To define the dynamic organization of the neuromuscular system, we need useful tools that allow for the expression of the neuromuscular system in low dimensional term (i.e one variable), so it seems that relative phase provides a better measure of organization of the neuromuscular system. Besides, selection of a measure for research or clinical use should be motivated by several factors, including the measure reliability. To our knowledge there seems to exist no study that have ever investigated the reliability of the relative phase and deviation phase in healthy or Low back pain subjects in dynamic movement tasks. Twelve healthy volunteers and 12 low back pain patients performed repeated trunk bending motion in eight different conditions of high and low speed, in symmetric and asymmetric planes, with or without external load. All measurements were repeated on a second session, 7-10 days later. Mean absolute relative phase and deviation phase of lumbar-thorax and pelvis-lumbar were used to calculate coordination pattern and variability. Relative reliability was assessed using intra class correlation coefficient (ICC) and absolute reliability was assessed using standard error measurement, minimum detectable change and coefficient of variation. Results in healthy subjects revealed that relative phase and deviation phase showed good to excellent reliability, with ICC range of 5.3-8.4 and in low back pain group ICC range was0 /52-0/85 except in three asymmetric test conditions and one symmetric test condition. SEM values range for healthy subjects were 0/92-4/8 and for low back patients were 1/2-5/8. Relative phase and deviation phase are suggested as good parameter to use for evaluating coordination and variability in dynamic situations such as lifting and complex trunk movement and also for discrimination low back pain patients from healthy subjects.