Pain Modulation Is Associated With Moderate Physical Activity In Gulf War Veterans With Chronic Pain

Abstract

Veterans of the Persian Gulf War (GV) suffer unresolved widespread chronic musculoskeletal pain (CMP) that significantly impacts their functional ability and quality of life. Pain modulation is impaired in some groups with CMP and can be augmented with acute exercise. Further, we have shown that physical activity behaviors in women with fibromyalgia are positively associated with pain modulation. Whether this relationship occurs in GV with CMP is unknown. PURPOSE: To examine the relationships between self-reported and accelerometer measures of physical activity and pain modulation in GV with CMP. METHODS: Sixty-eight GV with CMP were recruited and 55 completed physical activity assessments that included completing the International Physical Activity Questionnaire and wearing an Actigraph accelerometer for one week. Psychophysical pain testing was used to assess pain modulation. Painful heat stimuli were delivered alone and during completion of a distracting cognitive task, the Stroop Color and Word Test. Participants rated pain intensity and unpleasantness using Gracely Box Scales (0-20). Multiple linear regression analyses were used to determine whether physical activity significantly predicted pain responses during the distracting cognitive task while controlling for age (years), body mass index (BMI), pain symptom severity (McGill Pain Questionnaire), and mood (Profile of Mood States). RESULTS: Forty-three GV with CMP were included in the analyses (age = 50.0 (SD 6.7) years; weight = 100.7 (SD 37.2) kg; height = 1.7 meters (SD 8.3); Average Widespread Pain Index scores = 7.0 (SD 3.3)). Moderate physical activity (β=-0.45), based on accelerometer measurements, was a significant predictor of pain responses during distraction (F (5, 37) = 2.572, p < 0.05); adjusted R2 = 0.16. Relevant covariates (age, BMI, mood and pain symptom severity) were not significant predictors of pain ratings. Self-reported physical activity (β=-0.08) was not a significant predictor of pain responses during distraction (F (5, 45) = 1.298, p > 0.05). CONCLUSION: These results suggest that being physically active may help to maintain pain regulatory mechanisms in GV with CMP, but the strength of the relationship was weak and requires further research. Supported by US Department of Veterans Affairs grant #I01CX000383.