title: Influence of caffeine on metabolic and cardiovascular functions during sustained light intensity cycling and at rest.
abstract: This study assessed the influence of caffeine on metabolic and cardiovascular functions during sustained, light intensity cycling and at rest. Eight healthy, recreationally active adults participated in four randomly assigned, double-blind experimental trials of 60 min upright seated cycle exercise (30% VO2 max) or equivalent rest with caffeine (5 mg.kg-1) or placebo consumed 60 min prior to data collection. Gas exchange was measured by open-circuit spirometry indirect calorimetry. Global blood flow was evaluated by thoracic impedance cardiography and arterial blood pressure by auscultation. A repeated measures ANOVA indicated that pretrial caffeine increased oxygen uptake and energy expenditure rate (p < 0.05) but did not change respiratory exchange ratio. Systolic, diastolic, and mean arterial blood pressure were elevated following caffeine intake (p < 0.05). Cardiac output, heart rate, stroke volume, and systemic vascular resistance were not significantly different between caffeine and placebo sessions. For each of the metabolic and hemodynamic variables examined, the effects of caffeine were similar during constant-load, light intensity cycling and at rest. These data illustrate that caffeine's mild thermogenic influence can be mediated without a major shift in substrate oxidation mixture. Caffeine at this dosage level alters cardiovascular dynamics by augmenting arterial blood pressure.
authors.affiliation: Div. of HPR-Exercise Science, Wayne State University, Detroit, MI 48202, USA.
authors.forename: H J
authors.initials: HJ
authors.lastname: Engels
authors.forename: J C
authors.initials: JC
authors.lastname: Wirth
authors.forename: S
authors.initials: S
authors.lastname: Celik
authors.forename: J L
authors.initials: JL
authors.lastname: Dorsey
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001642:Bicycling; D002110:Caffeine / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D004311:Double-Blind Method; D004734:Energy Metabolism / Q000187:drug effects*; D015444:Exercise; D005260:Female; D006439:Hemodynamics / Q000187:drug effects*; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D012146:Rest; D013147:Spirometry
chemical_list: D000697:Central Nervous System Stimulants; D002110:Caffeine