title: No effect of nutritional adenosine receptor antagonists on exercise performance in the heat.
abstract: Nutritional adenosine receptor antagonists can enhance endurance exercise performance in temperate environments, but their efficacy during heat stress is not well understood. This double-blinded, placebo-controlled study compared the effects of an acute dose of caffeine or quercetin on endurance exercise performance during compensable heat stress (40 degrees C, 20-30% rh). On each of three occasions, 10 healthy men each performed 30-min of cycle ergometry at 50% Vo2peak followed by a 15-min performance time trial after receiving either placebo (Group P), caffeine (Group C; 9 mg/kg), or quercetin (Group Q; 2,000 mg). Serial blood samples, physiological (heart rate, rectal, and mean skin body temperatures), perceptual (ratings of perceived exertion, pain, thermal comfort, motivation), and exercise performance measures (total work and pacing strategy) were made. Supplementation with caffeine and quercetin increased preexercise blood concentrations of caffeine (55.62 +/- 4.77 microM) and quercetin (4.76 +/- 2.56 microM) above their in vitro inhibition constants for adenosine receptors. No treatment effects were observed for any physiological or perceptual measures, with the exception of elevated rectal body temperatures (0.20-0.30 degrees C; P < 0.05) for Group C vs. Groups Q and P. Supplementation did not affect total work performed (Groups P: 153.5 +/- 28.3, C: 157.3 +/- 28.9, and Q: 151.1 +/- 31.6 kJ; P > 0.05) or the self-selected pacing strategy employed. These findings indicate that the nutritional adenosine receptor antagonists caffeine and quercetin do not enhance endurance exercise performance during compensable heat stress.
authors.affiliation: U.S. Army Research Institute of Environmental Medicine, Thermal and Mountain Medicine Division, Kansas St., Natick, MA 01760-5007, USA. samuel.n.cheuvront@us.army.mil
authors.forename: Samuel N
authors.initials: SN
authors.lastname: Cheuvront
authors.forename: Brett R
authors.initials: BR
authors.lastname: Ely
authors.forename: Robert W
authors.initials: RW
authors.lastname: Kenefick
authors.forename: Bozena B
authors.initials: BB
authors.lastname: Michniak-Kohn
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Rood
authors.forename: Michael N
authors.initials: MN
authors.lastname: Sawka
mesh_terms: D000293:Adolescent; D000328:Adult; D001831:Body Temperature / Q000187:drug effects; D002110:Caffeine / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D019587:Dietary Supplements; D004311:Double-Blind Method; D006339:Heart Rate / Q000187:drug effects; D018882:Heat Stress Disorders / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D006358:Hot Temperature; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000187:drug effects*; D010101:Oxygen Consumption / Q000187:drug effects; D010465:Perception; D010807:Physical Endurance / Q000187:drug effects*; D058915:Purinergic P1 Receptor Antagonists; D011794:Quercetin / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D013997:Time Factors; D014882:Water-Electrolyte Balance; D055815:Young Adult
chemical_list: D058915:Purinergic P1 Receptor Antagonists; D002110:Caffeine; D011794:Quercetin