No Sex Differences In Conditioned Pain Modulation Or Exercise-induced Hypoalgesia Following Lower Body Isometric Exercise

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Women are more at risk than men for developing chronic pain conditions. Differences in endogenous pain-modulatory function could be a contributing factor. PURPOSE: The aim of this study was to compare conditioned pain modulation (CPM) and exercise-induced hypoalgesia (EIH) responses between adult men and women. METHODS: In a cross-sectional, non-randomized study with two independent groups of college aged males (n = 52) and females (n = 45), pressure pain thresholds (PPT) were assessed bilaterally in the vastus lateralis (VL) and brachioradialis (BR) muscles using a pressure algometer prior to and immediately following a conditioning stimulus (placing their foot in an ice bath) and performing isometric knee extension exercise to failure at 25% of maximal strength. RESULTS: Men had higher baseline PPTs than females (LBR: 372 ± 217 vs. 303 ± 119; RBR : 396 ± 236 vs. 315 ± 143; NDVL: 552 ± 281 vs. 434 ± 157 DVL: 572 ± 253 vs. 454 ± 147; P < 0.01). PPTs increased significantly (P < 0.05) following the conditioning stimulus in both males and females (LBR: 387 ± 264 to 453 ± 318 kPa, and 315 ± 126 to 359 ± 145 kPa; RBR: 400 ± 225 to 450 ± 280 kPa; and 325 ± 135 to 372 ± 161 kPa; DVL; 579 ± 289 to 658 ± 349 kPa;, and 470 ± 200 to 541 ± 201 kPa; NDVL 542 ± 263 to 623 ± 326 kPa; and 433 ± 174 to 503 ± 185 kPa in the in the males and females, respectively) indicating a CPM response in all limbs tested. PPTs increased significantly (P < 0.05) following isometric knee extension exercise to a similar extent in both males and females in all limbs tested (LBR: 387 ± 177 to 466 ± 245 kPa; and 305 ± 140 to 353 ± 162 kPa; RBR: 409 ± 172 to 462 ± 228 kPa; and 312 ± 147 to 355 ± 173 kPa. DVL: 572 ± 253 to 763 ± 366 kPa; and 454 ± 147 to 611 ± 252 kPa; NDVL: 552 ± 281 to 633 ± 353 kPa and 434 ± 157 to 526 ± 210 kPa) There was no interaction between the group x testing site for either the CPM response (P = 0.314) or the EIH response (P = 0.242). CONCLUSIONS: Men had a higher resting pain threshold than women. However, men and women exhibited similar endogenous pain inhibitory function both locally and systemically following a conditioning stimulus and isometric lower body exercise.