The effects of caffeine ingestion on exercise-induced hypoalgesia: A pilot study

Exercise acutely reduces pain sensitivity, termed exercise-induced hypoalgesia (EIH). The mechanisms underlying EIH remain unclear. Caffeine, a non-specific adenosine receptor antagonist has been shown to attenuate EIH in animals suggesting the involvement of the adenosinergic system. This pilot study investigated the effects of caffeine on pain sensitivity following cycling exercise in college-aged men. Pressure pain threshold (PPT) and thermal pain threshold (TPT) were assessed in thirteen low caffeine consuming men prior to ingestion of a counter-balanced 5 mg.kg(-1) dose of caffeine or a placebo (Pre), 60 min following ingestion (Post-In), and then following a 15 min bout of cycling exercise (Post-Ex) at an intensity eliciting a quadriceps muscle pain rating of 3 out of 10. Nine of the men completed follow-up testing which was identical except that the exercise consisted of 10 min of cycling eliciting a pain rating of 5 out of 10. Caffeine had no effect compared to placebo on PPT (p >= 0.15) or TPT (p >= 0.41) 60 min following ingestion and following exercise. PPT increased from 599 +/- 176 kPa to 648 +/- 202 kPa (p = 0.009) and from 578 +/- 217 kPa to 666 +/- 278 kPa (p = 0.01) following 15 and 10 min of cycling, respectively. TPT increased from 46.2 +/- 2.9 degrees C to 46.8 +/- 2.6 degrees C (p = 0.008) following the 15 min exercise bout, but did not change (46.4 +/- 3.6 degrees C vs. 46.8 +/- 3.3 degrees C; p = 0.24) following the shorter, higher intensity exercise bout. The results from this study indicate cycling exercise reduces pain sensitivity, especially to pressure stimuli. Caffeine ingestion did not alter the EIH response suggesting adenosine may not play a prominent role in the EIH response in humans. (C) 2016 Elsevier Inc. All rights reserved.