The Identification of Pain Phenotypes in Individuals With Low Back Pain in Response to Dynamic Resistance Exercise.

BACKGROUND

Exercise-induced hypoalgesia (EIH) describes an acute reduction in pain following exercise. Individuals with low back pain (LBP) demonstrate variable EIH responses, such as increased pain sensitivity (hyperalgesia). Pain phenotyping, classifying individuals with pain sensitivity and psychological characteristics, may explain this variability. LBP phenotypes were classified using pain sensitivity, psychological variables, and EIH response to dynamic resistance exercise.

METHODS

In this observational cohort study, 78 individuals with LBP (mean age = 21.7 ± 2.6 years, 59% female) completed clinical pain ratings (Numeric Pain Rating Scale [NPRS]), temporal summation (TS), conditioned pain modulation (CPM), psychological questionnaires (Fear-Avoidance Beliefs Questionnaire-Physical Activity subscale [FABQ-PA]), and a 45-degree Roman chair back extension exercise. Pressure pain threshold (PPT) pre- and post-exercise determined EIH. Ward's hierarchical cluster analysis was performed with five variables (NPRS, TS, CPM, FABQ-PA, EIH). One-way ANOVA examined differences in demographic, clinical, and psychosocial factors by cluster.

RESULTS

Three distinct clusters emerged: (1) efficient pain modulation with low fear-avoidance and high EIH (n = 40); (2) impaired pain modulation with moderate fear-avoidance and hyperalgesia (n = 19); (3) moderate pain modulation with high fear-avoidance and moderate EIH (n = 19). Clusters differed significantly by age (p = 0.02, ηp 2 = 0.098), disability (p = 0.004, ηp 2 = 0.138), psychosocial burden (p = 0.03, ηp 2 = 0.086), and pain catastrophizing (p = 0.03, ηp 2 = 0.09).

CONCLUSION

Individuals with LBP exhibit heterogeneous pain phenotypes. Psychological factors may diminish EIH, and impaired modulation may produce hyperalgesia post-exercise. Identifying pain phenotypes may enhance personalised rehabilitation strategies, optimising interventions for LBP.

SIGNIFICANCE: This study provides novel evidence that biopsychosocial phenotypes influence pain responses to resistance exercise, offering a potential pathway to personalised rehabilitation for LBP.