(305) The Contribution of Experimental Pain to the Sex Differences in Exercise-Induced Hypoalgesia

Abstract

The aim of this study was to investigate the effect of baseline (pre-exercise) temporal summation (TS) on the change of TS following submaximal isometric exercise in young healthy men (M) and women (W). Fifty-seven participants (20.75 ± 1.81 years; 29 women) completed two randomized sessions (exercise or quiet rest session). Isometric exercise consisted of sustained contraction of the knee extensors at 30% of maximum voluntary contraction performed until task failure. TS was assessed by applying a mechanical noxious stimulus equivalent to either 1kg (Low group) or 1.5 kg (High group) on the index finger. The mechanical noxious stimulus was applied for one minute beyond pain threshold, and subjects were instructed to rate their pain every 15 seconds on a numerical pain rating scale (0-10). TS was evaluated before and after exercise and quiet rest. The magnitude of TS was calculated as: [last pain rating – first pain rating]. The change of TS was compared between the two groups within each sex (M-High, M-Low, W-High, and W-Low). Sex differences in exercise-induced hypoalgesia (EIH) occurred among the high TS stimulus intensity group (session X trial X sex X group; p= 0.01); only W-High group experienced EIH while M-High experienced no change (session X trial X sex; p=0.039). Among women, the W-High had greater EIH than W-Low (session X trial X group; p= 0.049). In addition, pre-exercise TS was positively correlated with the magnitude of EIH (r= 0.34, p= 0.01). These results suggest that baseline experimental pain may contribute to the magnitude of EIH and to the sex differences in EIH.