Baseline Pain Summation Predicts Resting but Not Movement Pain Relief After Exercise in Low Back Pain

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BACKGROUND: Central modulatory pain mechanisms may influence improvements after exercise in low back pain (LBP). This observational study explored whether temporal summation of pain (TSP) and exercise-induced hypoalgesia (EIH) are associated with improvements in resting pain and movement-evoked pain, as it may improve the understanding of variation in effectiveness after an exercise program in individuals with LBP. METHODS: At baseline and after an 8-week exercise program, ratings of resting pain and movement-evoked pain on a 0-10 numerical rating scale (NRS) were assessed in 69 individuals with LBP. Cuff algometry at the lower leg (recording of the pain intensity to 10 repeated painful cuff stimulation) and pressure pain thresholds at the low back and leg immediately before and after a 6-min walking test were used to assess baseline TSP and EIH, respectively. Linear regression analyses adjusted for age and gender were used to assess the strength and direction of associations between baseline TSP and EIH with pain improvements (baseline minus Week 8). RESULTS: Resting-pain NRS scores were reduced by 0.9 (0.5-1.3) and movement-evoked pain by 0.9 (0.4-1.5) after 8 weeks of exercise. Higher baseline TSP was associated with improvement in resting pain (B = 0.29, p = 0.014), but not significantly with improvement in movement-evoked pain. Baseline EIH, regardless of the site point, was not significantly associated with resting or movement-evoked pain improvements. CONCLUSION: This study suggests that higher TSP at baseline is weakly but significantly associated with larger improvement in resting-pain intensity after an 8-week exercise program in people with LBP but this should be confirmed in larger studies. SIGNIFICANCE STATEMENT: Assessing central pain mechanisms may help identify individuals more likely to benefit from therapy, guiding personalised exercise-based treatments. Thus, this exploratory study provides preliminary evidence that higher baseline TSP is associated with greater improvements in resting pain following an exercise intervention. However, neither TSP nor EIH were associated with movement-evoked pain changes. These findings highlight the potential clinical relevance of evaluating central pain mechanisms when designing rehabilitation strategies for pain relief in LBP.

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