Influence Of Physical Activity And Sedentary Behavior On Anticipation-related Pain Sensitivity In Gulf War Veterans With Chronic Muscle Pain

Abstract

Exercise can alter pain sensitivity among Gulf War Veterans with chronic muscle pain (CMP). Anticipation of a painful experience can influence perceptual and neural responses to non-painful thermal stimuli among Fibromyalgia patients and this may extend to other patient groups with CMP. However, the association between physical activity or sedentary behavior and anticipation-related pain sensitivity has not been adequately studied. PURPOSE: To determine if (i) anticipation of pain influenced perceptual and neural responses to thermal stimuli among Veterans with CMP and (ii) anticipation-related pain sensitivity was associated with physical activity or sedentary behavior. METHODS: Gulf War Veterans with (n=29; 46±6.5 years) and without (n=29; 45±6.7 years) CMP were randomly assigned to conditions in which they were told that they would receive a painful or non-painful heat stimulus. Following one week of physical activity monitoring (ActiGraph GT3X), functional MRI responses to a 20-second warm stimulus (40C) applied to the left palm were measured on a 3T MRI scanner (GE MR750). Participants were then asked to provide ratings of pain intensity and unpleasantness following thermal stimulus administration. RESULTS: Factorial ANOVA with group and condition as between-subjects factors revealed significantly higher pain intensity (p =.003; d =.85) and unpleasantness (p =.006; d=0.76) ratings in the pain anticipation condition. A main effect for group and condition by group interaction was not found. Analyses of fMRI responses showed significantly different lateral postcentral gyrus activation in the pain anticipation condition. Linear regression analyses on Veterans in the pain anticipation condition showed that physical activity (e.g., moderate-vigorous physical activity) and sedentary behavior (e.g., average sedentary bouts of 30 or 60 minutes) did not significantly predict perception of pain intensity or unpleasantness. CONCLUSION: Pain anticipation influences perceptual and neural responses to non-painful stimuli among Gulf War Veterans with or without CMP; however, physical activity or sedentary behavior may not be related to anticipation-related pain sensitivity in this population. Supported by Dept. of Veterans Affairs grant: 561-00436