Resistance Training Demonstrates Acute Local Muscular Increases In Heat Pain Threshold

Exercise may acutely reduce pain perception of both the exercising muscle and systemically at distant, non-exercising sites. However, limited research has examined this phenomenon, exercise-induced hypoalgesia (EIH), with multiple noxious stimuli following dynamic resistance exercise. This investigation seeks to provide rationale to utilize dynamic resistance training for pain management and rehabilitation strategies. PURPOSE: To compare local and systemic changes in two noxious stimuli: pressure pain threshold (PPT) and heat pain threshold (HPT) after upper and lower body resistance exercise. METHODS: In a crossover study design, 28 participants (age: 21 ± 4 years, 21 female, 7 male) attended three testing sessions separated by a minimum of 48 hours. The first session consisted of baseline testing and a 5-repetition maximum (RM) strength test for the upper body (shoulder press) and lower body (leg extension). During the second and third session, participants completed an upper or lower body exercise in a counterbalanced order with weight equivalent to 75% of the estimated 1-RM for three sets of ten repetitions. To measure local and systemic effects of exercise on the perception of pain, HPT and PPT were applied to three sites (deltoid, quadriceps, low back) pre and post exercise. Three-way repeated measures analysis of variance examined time (pre/post) × location (quadriceps, deltoid, low back) × condition (upper/lower) effects. RESULTS: A significant three-way interaction for HPT was observed (F (1.71, 3.80) = 2.19, p = 0.036, η2p = 0.12). HPT significantly increased over the quadriceps after lower body exercise (F(1, 4.49) = 2.55, p = 0.043) and over the deltoid after upper body exercise (F(1, 11.88) = 12.31, p = 0.02), but not over the low back. PPT showed no interactions or main effects (p’s > 0.05). CONCLUSIONS: Significant EIH is present over the local, exercising muscle but not systemically after performing an acute bout of dynamic resistance training in healthy adults. Peripheral changes in pain sensitivity after exercise may be more responsive to heat stimuli, a primarily C-fiber mediated stimuli.