Relationship Among Site Specific Fat, Lean Mass, And Endogenous Pain Inhibitory Function

Abstract

Overweight individuals experience greater functional and psychological complications of chronic pain. Dysfunction of endogenous pain-modulatory mechanisms such as conditioned pain modulation (CPM) and exercise-induced hypoalgesia (EIH) have been found across a host of chronic pain conditions. PURPOSE: The purpose of the study was to assess endogenous pain inhibitory function and its relationship with whole body and site specific lean and fat mass. METHODS: PPT of 73 participants (38F; 35M) were assessed in the vastus lateralis (VL) and brachioradialis (BR) using a pressure algometer on both sides of the body before and after submersion of their feet in an ice bath (2°C) for 1min and an isometric knee extension, time to failure task based off of 25% of their maximal voluntary contraction. The difference between post and pre measures was defined CPM response (ice bath) and EIH response (exercise condition). Whole body and site specific fat and lean tissue were assessed via DXA scan, and muscle and fat thickness were assessed in the right (R) and left (L) VL and BR using ultrasound and skinfolds. RESULTS: Both CPM and EIH responses significantly increased PPTs for all of the four measured sites (p ≤ 0.001). BF% (r=0.256; p=0.029) and fat mass (r=.277; p=0.018) correlated with LBR CPM but not with site specific measures (p>0.05). RBR, RVL, and LVL CPM did not correlate with any measures of body composition (p>0.05). An inverse relationship was found between dominant VL EIH and whole body lean mass (r=-0.259; p=0.028), as well as limb specific lean mass (r=-0.262; p=0.026). No relationships were found between any of the body composition measures and non-dominant VL (p>0.05). CONCLUSION: It appears that in young, healthy adults, whole body and site specific fat mass does not influence endogenous pain-inhibitory function. However, having more lean tissue may have a negative effect on the EIH response. This may be due to larger muscle mass leading to a faster rate of fatigue, reducing exercise time which may have influenced the EIH response rather than muscle mass per se.