Exercise-induced Hypoalgesia Differ At Sites Local And Remote To The Exercising Muscle Group

Abstract

Dysfunction of endogenous pain-inhibitory function such as exercise-induced hypoalgesia (EIH) may predict development of chronic pain conditions. While EIH has been shown to occur in both the exercised muscle group and in remote unexercised muscle group, few studies have compared the magnitude of EIH in an exercised muscle and remote muscle groups in the same individuals following the same exercise bout. PURPOSE: The purpose of the study was to examine the EIH response at four different sites following a bout of single legged isometric exercise. METHODS: Pressure pain thresholds (PPT) of 102 participants (50 females; 52 males) were assessed bilaterally in the vastus lateralis (VL) and brachioradialis (BR) using a pressure algometer before and after isometric knee extension at 25% of maximal voluntary contraction held until task failure using their dominant leg. The percent difference between post and pre measures was defined the EIH response. RESULTS: PPT’s increased in the left BR (18.1% ± 24.7; p<0.001, d=0.275), right BR (14.4% ± 26.1; p<0.001, d=0.233), non-dominant VL (17.4% ± 24.0; p<0.001, d=0.318) and the dominant VL (34.5% ± 28.3; p<0.001, d=0.643). There were no differences between the left and right BR and the non-dominant VL with regards to the EIH response (p>0.05), however the exercised leg demonstrated a greater EIH response compared to the remote, unexercised limbs (p<0.001). CONCLUSION: EIH occurred in all sites. However the EIH response in the exercised leg was significantly more robust than the remote, unexercised sites. This findings suggests the magnitude of EIH is determined by both local and systemic factors and this should be taken into consideration when comparing EIH among studies.