Assessment of exercise-induced hypoalgesia in chronic low back pain and potential associations with psychological factors and central sensitization symptoms: A case-control study.

INTRODUCTION
Exercise is the most recommended treatment for chronic low back pain (CLBP) and is effective in reducing pain, but the mechanisms underlying its effects remain poorly understood. Exercise-induced hypoalgesia (EIH) may play a role and is thought to be driven by central pain modulation mechanisms. However, EIH appears to be disrupted in many chronic pain conditions and its presence in people with CLBP remains unclear. As people suffering from chronic pain often exhibit psychological factors and central sensitization symptoms influencing pain perception, EIH might be associated to these factors.


OBJECTIVE
To compare the level of EIH between participants with and without CLBP following back and wrist exercises and to assess the associations between EIH, psychological factors and central sensitization inventory score (CSI) in CLBP.


METHOD
Twenty-eight participants with CLBP and 23 without pain were recruited. Pressure pain thresholds (PPT) were measured at 4 sites (2 bony sites = capitate, S1 | 2 muscle sites = wrist flexors, lumbar erector spinae) before and after each of two exercises (wrist flexion and lumbar extension). EIH was defined as percent change in PPT from pre-to-post-exercise. Participants with CLBP also completed questionnaires to measure psychological factors (e.g. kinesiophobia, catastrophizing, anxiety, self-efficacy) and symptoms of central sensitization (CSI), and correlations with EIH was calculated.


RESULTS
After wrist exercise, EIH measured at the muscle sites was lower in the CLBP group compared to the pain-free group (p=0.047) but no differences were found at bony sites (p=0.49). No significant differences for EIH were observed following back exercise at muscle sites (p=0.14) or at bony sites (p=0.65). EIH was not correlated with any psychological factors or to the CSI score.


CONCLUSION
The lower EIH following wrist exercises may represent an alteration in pain modulation control in CLBP. However, psychological factors and central sensitization symptoms may not explain the differences observed.