1. Regular exercise reported at baseline was associated with less pain in repeated measures over a subsequent 12 month period, though this association was attenuated when adjusting for baseline level of pain.
2. Exercise was associated with a significant reduction in concurrent pain, though this association did not persist at 3 months.
Evidence Rating Level: 3 (Fair)
Study Rundown: Pain complaints – both acute and chronic – account for a substantial and costly burden of disease in the US. Clinical studies suggest a potentially causal relationship between exercise and pain relief in patients with fibromyalgia and low back pain. However, cross-sectional studies to examine the relationship between pain and exercise have been limited by the confounders that vary among individuals (socioeconomic status, genetic makeup) and vary across time for a given individual (mood, injuries). This study reduced the influence of confounders through within-subject analyses, and demonstrated a relationship between exercise and concurrent, but not future, pain levels. It also revealed an association between baseline exercise levels and pain measures. However, the effect sizes of these associations were quite small and thus likely statistically, but not clinically, significant. The most important conclusion to be drawn from this study may be one regarding study design and interpretation; namely, the importance of considering baseline pain level in prospective studies and, more generally, of considering confounders when interpreting cross sectional studies of association.
Relevant Reading: Exercises for prevention of recurrences of low-back pain.
In-Depth [Longitudinal population-based study]: The aim of this study was to investigate the association between exercise and pain longitudinally. The study looked at a random subsample of 6419 participants in the HUNT 3 study, which consisted of 3 cross-sectional surveys distributed to all inhabitants of a given county in Norway. Questionnaires were mailed to the subsample and participants were asked to report their last week pain and exercise every 3 months over a 12 month period. Linear regression analysis was used to evaluate a) whether baseline level of regular exercise was associated with pain levels in the 12 months of follow-up and b) how exercise and pain were associated within individuals over time. Within-subjects associations were estimated to limit confounding; instead of comparing groups of individuals who exercise to those who do not, the study compared an individual at time A to him/herself at time B.
After adjusting for age, sex, education, and smoking, those reporting at least moderate exercise 1–3 times a week in HUNT 3 reported 1.12 points less pain on the SF-8 scale (95% CI 0.60-1.63), as compared to those not reporting regular exercise. This difference was significantly attenuated when additionally adjusted for baseline level of pain (0.42, 95% CI 0.23-0.82). Within subjects analyses demonstrated a significant relationship between exercise intensity and concurrently reported pain intensity; a change from no to moderate exercise as associated with a 1.75 improvement in pain on the SF-8 scale. However, no association was seen between exercise at one occasion and pain measured three months later.
By Elizabeth Kersten and Andrew Bishara
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