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Study Title and Description

No effect of nutritional adenosine receptor antagonists on exercise performance in the heat.



Key Questions Addressed
1 For [population], is caffeine intake above [exposure dose], compared to intakes [exposure dose] or less, associated with adverse effects on cardiovascular outcomes?
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Primary Publication Information
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TitleData
Title No effect of nutritional adenosine receptor antagonists on exercise performance in the heat.
Author SN Cheuvront,BR Ely,RW Kenefick,BB Michniak-Kohn,JC Rood,MN Sawka,
Country
Year 2009
Numbers

Secondary Publication Information
There are currently no secondary publications defined for this study.


Extraction Form: Cardiovascular Design
Design Details
Question... Follow Up Answer Follow-up Answer
What outcome is being evaluated in this paper? Cardiovascular
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What is the objective of the study (as reported by the authors)? 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.
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Provide a general description of the methods as reported by the authors. Information should be extracted based on relevance to the SR (i.e., caffeine related methods) Subjects: Ten healthy, non-heat-acclimated male volunteers [mean (range): age 23 (18 –37) yr, body mass 77.5 (64.2–94.8) kg] participated in this study and completed all phases of experimentation. Subjects were physically active and moderately fit. A caffeine intake questionnaire was given, and anyone admittedly sensitive to caffeine or who consumed >400 mg/d was excluded from participation. Caffeine abstinence was required for 4 days before testing. Subjects were provided informational briefings and gave voluntary, informed written consent to participate. Experimental procedures: Volunteers were randomly assigned to complete three experimental trials [placebo (Group P), caffeine (Group C), quercetin (Group Q)] separated by 5–7 days each. All experiments were conducted at the same time of day to control for circadian fluctuations in body temperature and other biological variables. A fasting blood sample was drawn (baseline), after which volunteers were given a standardized breakfast including sports bars, gelatin capsules, and water. A second blood sample was drawn 1-h postbreakfast (preexercise). Volunteers were then instrumented in the 20–22°C antechamber (about 10 min) and weighed immediately upon entering the hot test environment. Following a seated 20-min stabilization period in the 40°C test environment, data collection was begun. Thirty minutes of steady-state cycle ergometry was completed at 50% VO2peak intensity. Heart rate (HR) (Polar a3; Polar Electro, Woodbury, NY) was recorded at 5-min intervals. Breakfast each day consisted of four cranberry-flavored energy bars (total energy = 557 kcal; 78% CHO, 18% fat, 4% protein), similar to commercially available sports bars. Other ingredients (sodium, potassium, chloride, calcium, vitamin C, and vitamin E) were well below ordinary U.S. Dietary Reference Intake levels. Volunteers also consumed between four and seven gelatin-coated capsules with about 500 ml water. The energy bars (Combat Feeding Directorate, U.S. Army Natick Soldier RDEC) were the delivery vehicle for food-grade quercetin aglycone powder (QU995; Quercegen Pharma, Newton, MA) equal to 500 mg/bar (2,000 mg total). The placebo bars contained no quercetin. The capsules delivered either USP anhydrous caffeine or microcrystalline cellulose (placebo) at 9 mg/kg. Capsules were formulated (Compounded Solutions in Pharmacy, Monroe, CT) to contain from 5 to 200 mg each to allow precision (+/-0.1 mg/kg) dosing. Volunteers received the placebo capsules and placebo bars (Group P), caffeine capsules and placebo bars (Group C), or placebo capsules and quercetin bars (Group Q). Treatment and placebo bars and capsules were indistinguishable by flavor and by ordinary inspection. Treatments were double blinded, and trial order was determined using a Latin square assignment. The doses for both caffeine and quercetin were estimated to elicit blood concentrations in excess of the in vitro inhibition constant (Ki) for adenosine receptor antagonism (caffeine, about 25 uM; quercetin, about 2.5 uM).
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How many outcome-specific endpoints are evaluated? 1
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What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately) Heart rate
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List additional health endpoints (separately). 2
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List additional health endpoints (separately).3
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List additional health endpoints (separately).4
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List additional health endpoints (separately).5
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List additional health endpoints (separately).6
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Clinical, physiological, other Physiological
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What is the study design? Controlled Trial
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Randomized or Non-Randomized? RCT
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What were the diagnostics or methods used to measure the outcome? Objective
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Optional: Name of Method or short description Heart rate (HR) (Polar a3; Polar Electro, Woodbury, NY) was recorded at 5-min intervals.
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Caffeine (general) Caffeine (general)
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Coffee, Chocolate, energy drink, gum, medicine/supplement, soda, tea, other?
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Measured or self reported? Measured
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Children, adolescents, adults, or pregnant included? Adults
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What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.) Volunteers received the placebo capsules and placebo bars (Group P), caffeine capsules and placebo bars (Group C), or placebo capsules and quercetin bars (Group Q). Treatment and placebo bars and capsules were indistinguishable by flavor and by ordinary inspection. Treatments were double blinded, and trial order was determined using a Latin square assignment.
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What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models.  Copy from methods) The effects of treatment (caffeine, quercetin, placebo) on outcome variables of interest was assessed using a one-way (trial) or two-way (trial x time) repeated-measures ANOVA. Where the assumption of sphericity was violated, F values were adjusted using Greenhouse-Geisser or Huynh-Feldt corrections as appropriate. Tukey’s honestly significant difference procedure was used to identify differences among means following significant main and/or interaction effects. Where indicated, the error uniformity of some variables was tested using regression analysis.
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What conflicts of interest were reported? The authors stated, "The opinions or assertions contained herein are the private views of the authors and should not be construed as official or reflecting the views of the Army of the Department of Defense."
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Refid 19020291
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What were the sources of funding? This research was supported, in part, by funding from the Defense Advanced Research Projects Agency and U.S. Army Contract W911QY-07-C-0027.
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Results & Comparisons

No Results found.