title: The effects of caffeine ingestion on exercise-induced hypoalgesia: A pilot study.
abstract: 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 5mg·kg(-1) dose of caffeine or a placebo (Pre), 60min following ingestion (Post-In), and then following a 15min 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 10min 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) 60min following ingestion and following exercise. PPT increased from 599±176kPa to 648±202kPa (p=0.009) and from 578±217kPa to 666±278kPa (p=0.01) following 15 and 10min of cycling, respectively. TPT increased from 46.2±2.9°C to 46.8±2.6°C (p=0.008) following the 15min exercise bout, but did not change (46.4±3.6°C vs. 46.8±3.3°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.
authors.affiliation: University of Oklahoma, Department of Health and Exercise Science, Norman, OK 73019, USA. Electronic address: cblack@ou.edu.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Black
authors.affiliation: University of Oklahoma, Department of Health and Exercise Science, Norman, OK 73019, USA.
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Gonglach
authors.affiliation: University of Oklahoma, Department of Health and Exercise Science, Norman, OK 73019, USA.
authors.forename: Jessica B
authors.initials: JB
authors.lastname: Renfroe
authors.affiliation: University of Oklahoma, Department of Health and Exercise Science, Norman, OK 73019, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Hight
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D002110:Caffeine / Q000378:metabolism* / Q000627:therapeutic use; D000697:Central Nervous System Stimulants / Q000378:metabolism* / Q000627:therapeutic use; D018592:Cross-Over Studies; D004311:Double-Blind Method; D015444:Exercise; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D006987:Hypesthesia / Q000188:drug therapy* / Q000209:etiology*; D008297:Male; D017288:Pain Threshold / Q000502:physiology; D010812:Physical Stimulation / Q000009:adverse effects; D010865:Pilot Projects; D013997:Time Factors; D055815:Young Adult
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine
keywords: Cycling; Pressure pain threshold; Thermal pain threshold