title: No effect of caffeine on exercise performance in high ambient temperature.
abstract: Caffeine, an adenosine receptor antagonist, has shown to improve performance in normal ambient temperature, presumably via an effect on dopaminergic neurotransmission through the antagonism of adenosine receptors. However, there is very limited evidence from studies that administered caffeine and examined its effects on exercise in the heat. Therefore, we wanted to study the effects of caffeine on performance and thermoregulation in high ambient temperature. Eight healthy trained male cyclists completed two experimental trials (in 30°C) in a double-blind-randomized crossover design. Subjects ingested either placebo (6 mg/kg) or caffeine (6 mg/kg) 1 h prior to exercise. Subjects cycled for 60 min at 55% W (max), immediately followed by a time trial to measure performance. The significance level was set at p < 0.05. Caffeine did not change performance (p = 0.462). Rectal temperature was significantly elevated after caffeine administration (p < 0.036). Caffeine significantly increased B-endorphin plasma concentrations at the end of the time trial (p = 0.032). The present study showed no ergogenic effect of caffeine when administered 1 h before exercise in 30°C. This confirms results from a previous study that examined the effects of caffeine administration on a short (15 min) time trial in 40°C. However, caffeine increased core temperature during exercise. Presumably, the rate of increase in core temperature may have counteracted the ergogenic effects of caffeine. However, other factors such as interindividual differences in response to caffeine and changes in neurotransmitter concentrations might also be responsible for the lack of performance improvement of caffeine in high ambient temperature.
authors: Department of Human Physiology and Sports Medicine, Faculty of Physical Education and Physiotherapy, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium.
authors: Bart
authors: B
authors: Roelands
authors: Luk
authors: L
authors: Buyse
authors: Frank
authors: F
authors: Pauwels
authors: Frans
authors: F
authors: Delbeke
authors: Koen
authors: K
authors: Deventer
authors: Romain
authors: R
authors: Meeusen
mesh_terms: D000328:Adult; D001642:Bicycling / Q000523:psychology; D001831:Body Temperature / Q000187:drug effects / Q000502:physiology; D001833:Body Temperature Regulation / Q000187:drug effects* / Q000502:physiology; D002110:Caffeine / Q000008:administration & dosage*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006358:Hot Temperature; D006801:Humans; D008297:Male; D055815:Young Adult; D001615:beta-Endorphin / Q000097:blood
chemical_list: D002110:Caffeine; D001615:beta-Endorphin