Changes in movement variability and complexity may reflect an adaptation strategy to fatigue. One unresolved question is whether this adaptation is hampered by the presence of low back pain (LBP). This study investigated if changes in movement variability and complexity after fatigue are influenced by the presence of LBP. It is hypothesised that pain free people and people suffering from LBP differ in their response to fatigue. The effect of an isometric endurance test on lumbar movement was tested in 27 pain free participants and 59 participants suffering from LBP. Movement variability and complexity were quantified with %determinism and sample entropy of lumbar angular displacement and velocity. Generalized linear models were fitted for each outcome. Bayesian estimation of the group-fatigue effect with 95% highest posterior density intervals (95%HPDI) was performed. After fatiguing %determinism decreased and sample entropy increased in the pain free group, compared to the LBP group. The corresponding group-fatigue effects were 3.7 (95%HPDI: 2.3-7.1) and -1.4 (95%HPDI: -2.7 to -0.1). These effects manifested in angular velocity, but not in angular displacement. The effects indicate that pain free participants showed more complex and less predictable lumbar movement with a lower degree of structure in its variability following fatigue while participants suffering from LBP did not. This may be physiological responses to avoid overload of fatigued tissue, increase endurance, or a consequence of reduced movement control caused by fatigue.

Pattern tracing tasks can be used to assess cervical spine movement sense (CMS). A simple clinical measure of CMS (tracing fixed figure-of-eight (F8) and zigzag (ZZ) patterns with a head mounted laser) has been proposed and assessed in asymptomatic subjects. It is important to determine if examiner ratings of the traces are reliable and feasible for clinical use in those with neck pain. We therefore examined the intra- and inter-rater reliability of rating video recordings of the CMS tasks, and the feasibility of undertaking the tests in clinic by comparing slow motion versus real-time video ratings. Cross-sectional study examining neck pain subjects from a physiotherapy clinic. F8 and ZZ patterns traced with a head-mounted laser pointer at two velocities (accurate; accurate & fast) were videoed and later examined. Time (total time taken to complete the pattern), error frequency (number of deviations) and error magnitude (sum of deviations multiplied by distance from the central line) were measured. Two assessors independently evaluated the laser tracing videos in slow motion; a third rated the videos in real time. Intraclass correlation coefficients (ICC) and standard error of measurements (SEM) were calculated for intra- and inter-tester reliability, and feasibility. Twenty neck pain patient (13 women) videos were assessed. Intra-and inter-rater reliability was substantial to almost-perfect (ICC 0.76–1.00; SEM < 0.01–2.50). Feasibility was moderate to almost-perfect (ICC 0.54–1; SEM < 0.01–2.98). Video (slow motion) ratings of time and errors for F8 and ZZ movement patterns in neck pain subjects showed high intra and inter-rater reliability. Achieving reliable ratings in clinic (real-time) appears feasible. Synthesising our results, the most reliable and feasible CMS ratings appear to be when the subject uses accurate rather than accurate and fast execution. The ZZ movement pattern may be superior to F8 in terms of rating. Time and error frequency for tracing F8 and ZZ as accurately as possible in determining CMS appears promising for use in clinic. Future research directions were identified.

Accurate measurements of spinal movement require reliable determination of anatomical landmarks. Current methods of identifying these are not sufficiently reliable or valid for this purpose. A reliable and convenient method of placing markers on selected vertebra is needed to compare measurements between different testers, subjects and sessions.