Body composition does not influence conditioned pain modulation and exercise-induced hyperalgesia in healthy males and females

Background Obese individuals report a higher susceptibility to chronic pain. Females are more likely to have chronic pain and excess adipose tissue. Chronic pain is associated with dysfunctional pain-modulatory mechanisms. Body composition differences may be associated with pain modulation differences in males and females. The purpose of this study was to investigate body composition (lean vs fat mass) differences and pain-modulatory functioning in healthy males and females. Methods Pressure pain thresholds (PPT) of 96 participants (47 M; 49F) were assessed in both arms and legs before and after a double-footed ice bath (2 degrees C) for 1 min and an isometric knee extension, time to failure task. The difference between post- and pre-measures was defined as conditioned pain-modulatory (CPM) response (ice bath) and exercise-induced hypoalgesia (EIH) response. Whole-body and site-specific fat and lean tissue were assessed via the DXA scan. Results Sex differences were found in whole-body lean mass (61.5 +/- 6.7 kg vs 41.2 +/- 5.4 kg; p < 0.001) but not fat mass amount (17.2 +/- 10.5 kg vs 21.0 +/- 9.7 kg; p = 0.068). No effect of sex was found between limb CPM (p = 0.237) and limb EIH (p = 0.512). When controlling for lean mass, there was no significant effect of sex on CPM (p = 0.732) or EIH (p = 0.474) response. Similar findings were found for fat mass. Conclusion The lack of difference suggests that males and females have similar modulatory functioning. It appears that in healthy adults free from chronic pain, neither fat mass nor lean mass has an influence on endogenous pain-modulatory function. Significance Men and women exhibited similar CPM and EIH despite marked differences in body composition. Our findings suggest whole-body and limb-specific lean tissue mass and fat mass do not influence CPM and EIH in adults without chronic pain.