Pain Modulation in Response to Resistance Exercise Training in Gulf War Veterans with Chronic Pain

Abstract

United States military Veterans of the Persian Gulf War (GV) suffer unresolved 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. Whether chronic exercise training influences pain modulation in GV with CMP is unknown. PURPOSE: To examine the effects of a 16-week resistance exercise training (RET) program on pain modulation in GV with CMP. METHODS: Forty GV with CMP were randomly assigned to RET (n=19) or a wait-list control group (WLC; n=21). The RET program was individualized to begin at a low intensity and involved standardized progression. Pain modulation was evaluated at baseline and 3 subsequent time points by comparing pain ratings to a series of painful heat stimuli delivered alone or concurrently with the Stroop color word task, which has two levels of cognitive difficulty: congruent (CS) and incongruent (IS). Variance to mean ratios (VMR) of pain modulation scores were calculated as an indicator of dispersion. Separate repeated measures MANOVA were used to examine the effect of group (RET vs. WLC) and time (1-4) on pain modulation (change in pain ratings) for both types of Stroop presentation. RESULTS: Groups did not differ on age, height, weight, or gender (p < 0.05). Whole body strength improved with training (average 1-RM% change from baseline across 10 upper & lower body exercises = 28.95%). No significant main or interaction effects were detected for either Stroop presentation (p > 0.05). The proportion of individuals demonstrating a pain modulatory response did not differ at any time point, X2 (1, N=40) = 0.14-2.10, p > 0.05. Pain modulation scores where highly variable for both groups across each time point (VMR Range: CS 1.77-1.96; IS 2.74-5.07). CONCLUSION: The degree to which GVs with CMP modulate pain at baseline does not appear to change as a result of RET, however pain modulation scores were highly variable across groups and time points. The lack of a change in pain modulation suggests that resistance exercise training in GVs with CMP does not influence the pain regulatory mechanism assessed here. Supported by US Department of Veterans Affairs grant #I01CX000383.