Effects of caffeine and high ambient temperature on haemodynamic and body temperature responses to dynamic exercise

Charles L Stebbins, Jason W. Daniels, William R Lewis

Research output: Contribution to journalArticle

22 Scopus citations

Abstract

Caffeine can enhance mean arterial blood pressure (MAP) and attenuate forearm blood flow (FBF) and forearm vascular conductance (FVC) during exercise in thermal neutral conditions without altering body temperature. During exercise at higher ambient temperatures, where a greater transfer of heat from the body core to skin would be expected, caffeine-induced attenuation of FBF (i.e. cutaneous blood flow) could attenuate heat dissipation and increase body temperature (Tre). We hypothesized that during exercise at an ambient temperature of 38°C, caffeine increases MAP, and attenuates FBF and FVC such that Tre is increased. Eleven caffeine-naive, active men, were studied at rest and during exercise after ingestion of a placebo or 6 mg kg-1 of caffeine. MAP, heart rate (HR), FBF, FVC, Tre skin temperature (Tsk) and venous lactate concentrations (lactate) were assessed sequentially during rest at room temperature, after 45 min of exposure to an ambient temperature of 38°C, and during 35 min of submaximal cycling. Heat exposure caused increases in MAP, FBF, FVC and Tsk that were not altered by caffeine. HR, Tre, and lactate were unaffected. During exercise, only MAP (95 ± 2 vs. 102 ± 2 mmHg), HR (155 ± 10 vs. 165 ± 10 beats min-1), and lactate (2.0 ± 0.4 vs. 2.3 ± 0.4 mmol l-1) were increased by caffeine. These data indicate that increases in cutaneous blood flow during exercise in the heat are not reduced by caffeine. This may be because of activation of thermal reflexes that cause cutaneous vasodilation capable of offsetting caffeine-induced reductions in blood flow. Caffeine-induced increases in lactate, MAP and HR during exercise suggest that this drug and high ambient temperatures increase production of muscle metabolites that cause reflex cardiovascular responses.

Original languageEnglish (US)
Pages (from-to)528-533
Number of pages6
JournalClinical Physiology
Volume21
Issue number5
DOIs
StatePublished - 2001

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Keywords

  • Bicycle ergometry
  • Blood pressure
  • Forearm blood flow
  • Forearm conductance
  • Thermal reflexes

ASJC Scopus subject areas

  • Physiology

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