Kuithan P1, Heneghan NR1, Sanderson A1, Rushton A1, Falla D1
1University of Birmingham, School of Sport, Exercise and Rehabilitation Sciences, Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), Birmingham, United Kingdom

Background: Exercise is the recommended management for chronic low back pain (cLBP) but consensus on the optimal type and dosage of exercise has not been reached. In healthy people, exercise induced hypoalgesia (EIH), a temporary increase of pain thresholds following exercise is reported. However, in some people with cLBP, occupational exercise tasks such as repetitive lifting are pain provocative suggesting that EIH may be absent in people with cLBP. Yet only a few studies have examined EIH in people with cLBP and to date, no studies have targeted the back muscles with an exercise or occupational task.

Purpose: To investigate whether quantitative sensory testing (QST) reveal dysfunctional EIH in individuals with cLBP following a simulated occupational lifting task.

Methods: A cross-sectional, observational study recruiting participants with cLBP and healthy controls was conducted in a university setting following ethical approval. Local and remote pressure and thermal thresholds, and remote temporal summation of pain were evaluated using QST. Local pressure pain thresholds (PPT) were recorded over 16 sites across the lower back. The task comprised lifting a 5kg box for ~7 minutes in a multidimensional rotational pattern. Perceived exertion and pain were quantified throughout the task. Data were analysed using a Repeated Measures Analysis of Variance with group, time and location as factors; followed by a Student-Newman-Keuls (SNK) post hoc test.

Results: Participants [12 women, 9 men, aged 31.7(SD 13.3) years] with mild cLBP [Oswestry Disability Index=15.5(7.2)] and asymptomatic participants [10 women, 8 men, age 28.2(12.5)] were recruited. The task was perceived as more fatiguing by participants with cLBP [Borg Scale=13.1(1.7) compared to [11.1(2.2)] and higher peak pain intensities during lifting were reported [NRS 4.8/10(2.0) compared to 0.8(2.0)]. Baseline QST measurements were comparable between groups. Local PPT was dependent on test location (F=10.8, p .00), and the interaction between location and group (F=1.9, p .03), location and time (F=2.9, p .00) and group and time (F=6.8, p .01). Further post hoc analysis revealed that lumbar PPT across all locations changed significantly by + 9.43% (13.4) for the asymptomatic group [pre 341.39kPa (116.9); post 371.16kPa (130.4); SNK: p= .019] whereas for the symptomatic group there was no significant change [-2.10% (18.4); pre 320.08kPa (113.7); post 305.20kPa (101.0); SNK: p> .05]. No remote change and no signs of temporal summation of pain occurred. Sensitivity to temperature did not change for either group.

Conclusion(s): Our findings show that EIH was lacking in participants with cLBP compared to asymptomatic participants. Further research is required to elucidate the mechanisms of EIH and the effect of different occupational exercise tasks targeted towards affected regions, as well as their interactions with perceived pain during exercise as this may have an impact on treatment outcomes.

Implications: This is the first study to illustrate that individuals with mild levels of cLBP and disability show altered EIH. This provides evidence to support further research investigating PPT as a clinical tool to detect impaired EIH in people with cLBP.

Keywords: Exercise Induced Hypoalgesia, Chronic Low Back Pain, Quantitative Sensory Testing

Funding acknowledgements: This work was unfunded.

Topic: Musculoskeletal: spine; Pain & pain management; Musculoskeletal

Ethics approval required: Yes
Institution: University of Birmingham (UK)
Ethics committee: Local Ethics committee of the University of Birmingham
Ethics number: ERN_16-1389

All authors, affiliations and abstracts have been published as submitted.

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