Effects of Muscle Fatigue, Creep, and Musculoskeletal Pain on Neuromuscular Responses to Unexpected Perturbation of the Trunk: A Systematic Review

Introduction: Trunk neuromuscular responses have been shown to adapt under the influence of muscle fatigue, as well as spinal tissue creep or even with the presence of low back pain (LBP). Despite a large number of studies exploring how these external perturbations affect the spinal stability, characteristics of such adaptations remains unclear. Aim: The purpose of this systematic review was to assess the quality of evidence of studies investigating trunk neuromuscular responses to unexpected trunk perturbation. More specifically, the targeted neuromuscular responses were trunk muscle activity reflex and trunk kinematics under the influence of muscle fatigue, spinal creep, and musculoskeletal pain. Methods: A research of the literature was conducted in Pubmed, Embase, and Sport-Discus databases using terms related to trunk neuromuscular reflex responses, measured by electromyography (baseline activity, reflex latency, and reflex amplitude) and/or trunk kinematic, in context of unexpected external perturbation. Moreover, independent variables must be either trunk muscle fatigue or spinal tissue creep or LBP. All included articles were scored for their electromyography methodology based on the “Surface Electromyography for the Non-Invasive Assessment of Muscles (SENIAM)” and the “International Society of Electrophysiology and Kinesiology (ISEK)” recommendations whereas overall quality of articles was scored using a specific quality checklist modified from the Quality Index. Meta-analysis was performed on reflex latency variable. Results: A final set of 29 articles underwent quality assessments. The mean quality score was 79%. No effect of muscle fatigue on erector spinae reflex latency following an unexpected perturbation, nor any other distinctive effects was found for back muscle fatigue and reflex parameters. As for spinal tissue creep effects, no alteration was found for any of the trunk reflex variables. Finally, the meta-analysis revealed an increased erector spinae reflex latency in patients with chronic LBP in comparison with healthy controls following an unexpected trunk perturbation. Conclusion: The literature provides some evidence with regard to trunk adaptions in a context of spinal instability. However, most of the evidence was inconclusive due to a high methodological heterogeneity between the studies.


Appendix B
Item 1. Is the hypothesis/aim/objective of the study clearly described? Yes = 1 / No = 0 When hypothesis was mentioned, a score of 1 was only attributed if the authors have stated a bi or unidirectional hypothesis.
Item 2. Are the main EMG reflex response outcomes to be measured clearly described in the methods section? Yes = 1 / No = 0 If the main outcomes are first mentioned in the Results section, the question should be answered no. Only the outcomes of interest were considered to answer this question.
Item 3. Are the characteristics of the participants included in the study clearly described? Yes = 1 / No = 0 If there were two or more groups, inclusion/exclusion criteria should be given for all groups. A minimum of 3 relevant criteria should be given for each group to attribute a score of 1. Criteria should answer the question [1] if participants experienced or not back pain, [2] for how long they had back pain or for how long they did not have back pain, and [3] if they had any medical condition?
Item 4.1. Are the perturbation protocol clearly described? Yes = 1 / No = 0 Item 4.2. Are the protocol of either muscle fatigue, or spinal creep or experimental pain clearly described? Yes = 1 / No = 0 Item 6. Are the main EMG reflex response findings of the study clearly described? Yes = 1 / No = 0 Item 7. Does the study provide estimates of the random variability in the data for the main outcomes? Yes = 1 / No = 0 In non-normally distributed data the inter-quartile range of results should be reported. In normally distributed data the standard error, standard deviation or confidence intervals should be reported. If the distribution of the data is not described, it must be assumed that the estimates used were appropriate and the question should be answered yes.
Item 10. Have actual probability values been reported (e.g. 0.035 rather than <0.05) for the main outcomes except where the probability value is less than 0.001? Yes = 1 / No = 0 Item 12. Were those subjects who participated representative of the entire population from which they were recruited? Yes = 1 / No = 0 / Unable to determine = 0 The study must identify the source population for patients. Where a study does not report the proportion of the source population from which the patients are derived, the question should be answered as unable to determine.
Item 16. If any of the results of the study were based on "data dredging", was this made clear? Yes = 1 / No = 0 / Unable to determine = 0 Any analyses that had not been planned at the outset of the study should be clearly indicated. If no retrospective unplanned subgroup analyses were reported, then answer yes.
Item 18. Were the statistical tests used to assess the main outcomes appropriate? Yes = 1 / No = 0 The statistical techniques used must be appropriate to the data. If the distribution of the data (normal or not) is not described it must be assumed that the estimates used were appropriate and the question should be answered yes. Statistical analysis plan should correspond to the proposed experiment. When multiple comparison are done, post hoc or planned comparison must be present. The use of covariable must be justified.