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Hermann-J. Engels, John C. Wirth, Sueda Celik, and Jodee L. Dorsey

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% VO2max) 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 spirom-etry 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.

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Rory Warnock, Owen Jeffries, Stephen Patterson, and Mark Waldron

Taurine, a sulfur-containing amino acid, is 1 of the primary ingredients in the most popular energy drinks. 1 In addition, most energy drinks contain caffeine, a methylxanthine drug commonly consumed by athletes as an ergogenic aid. 2 Caffeine ingestion (3–6 mg/kg body mass) has been shown to

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Craig Pickering and Jozo Grgic

coffee, decaffeinated coffee, and decaffeinated coffee with caffeine capsules, consumed ~60 min prior to the exercise trial. The caffeine dose was standardized across trials to deliver 4.45 mg/kg of caffeine, with a total volume of liquid of 7.15 ml/kg. Despite similar changes in plasma methylxanthines

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Alex M. Ehlert, Hannah M. Twiddy, and Patrick B. Wilson

). e33807 . doi:10.1371/journal.pone.0033807 10.1371/journal.pone.0033807 Mumford , G.K. , Benowitz , N.L. , Evans , S.M. , Kaminski , B.J. , Preston , K.L. , Sannerud , C.A. , . . . Griffiths , R.R. ( 1996 ). Absorption rate of methylxanthines following capsules, cola and chocolate

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Romain Meeusen and Lieselot Decroix

plants found in the Amazon, and it contains theophylline, theobromine, and caffeine. Theobromine is a methylxanthine that is an adenosine receptor antagonist (as caffeine) and might improve cognitive function. Two studies ( Haskell et al., 2007 ; Kennedy et al., 2004 ) have investigated the effects of