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Study Title and Description

Hydration during exercise in warm, humid conditions: effect of a caffeinated sports drink.



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 Hydration during exercise in warm, humid conditions: effect of a caffeinated sports drink.
Author ML Millard-Stafford,KJ Cureton,JE Wingo,J Trilk,GL Warren,M Buyckx,
Country
Year 2007
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)? The purpose of the present study was to investigate 1) fluid delivery using a relative index that reflects both gastric emptying and intestinal absorption and 2) other hydration-related parameters of a caffeinated sports drink compared with a noncaffeinated sports drink.
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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 Sixteen healthy, highly trained male cyclists were recruited and studied at 2 institutions (10 at the University of Georgia and 6 at Georgia Institute of Technology). Subjects trained an average (+/- SD) of 264 +/- 125 km/wk of cycling for 6 mo before the study. Mean (+/- SD) age, height, weight, percentage fat estimated from skinfolds, and maximal oxygen uptake (VO2max) were 27.5 +/- 7.0 y, 177.0 +/- 5.9 cm, 72.7 +/- 6.4 kg, 12.2% +/- 4.6%, and 60.5 +/- 7.2 mL/kg–min, respectively. All subjects habitually ingested caffeine, but daily intake varied from 9 to 482 mg, averaging 150 +/- 113 mg. Research Design A double-blind, placebo-controlled, repeated-measures experimental design was used, in which all subjects were tested under all conditions. After a preliminary test session in which subjects had VO2max measured and were familiarized with test procedures, 3 experimental trials were completed in random order, separated by at least 5 d. During an experimental trial, 1 of 3 beverage treatments was administered before and during 2 h of cycling at a standardized intensity (60% and 75% VO2max), followed immediately by a 15-min self-selected-pace ride at maximal effort. All trials took place in an environmental chamber at 28.5oC, 60% relative humidity, with fan airflow ~2.5 m/s. After cycling, subjects recovered for 20 min in normal laboratory conditions (21oC, 40% relative humidity). Treatments Three experimental beverages were used: 1) an artificially sweetened (aspartame), flavored water placebo control; 2) a commercially available 6% carbohydrate-electrolyte formulation (CE; Gatorade, Quaker Oats Co, Barrington, IL); and 3) a 7% commercially available carbohydrate-electrolyte beverage (Powerade, The Coca-Cola Company, Atlanta, GA) containing vitamins B3, B6, and B12; 46 mg/L carnitine; 1.92 g/L taurine; and 195 mg/L caffeine (CAF+CE). Beverages administered on a given day were placed in uniform plastic containers identifiable to investigators and subjects only by numerical code. Subjects ingested half of a pre-exercise bolus of 6 mL/kg body weight 10 min before exercise and the other half immediately before exercise. During cycling, subjects ingested 3 mL/kg body weight (220 mL on average) of beverage at 15-min intervals. Total caffeine ingestion during the CAF+CE trial was 1.2 mg/kg before exercise, 3.5 mg/kg after 60 min, and 5.3 mg/kg for the entire protocol. Protocol and Procedures Preliminary Test Session: Body mass was measured to the nearest 10 g with an electronic scale (model FW-150KA1, A&D Co, Ltd, Tokyo). A graded exercise test was conducted to measure VO2max on an electronically braked cycling ergometer (Lode Excalibur Sport, Lode BV, Groningen, The Netherlands). Heart rate (HR) was measured every 2 min and at the end of the VO2max test with a Polar Vantage XL monitor (model 145900, Polar Electro, Inc, Woodbury, NY). The practice session concluded with 15 min of cycling in which subjects performed as much work as possible to become familiar with the maximal-effort performance. Experimental Controls: Participants were instructed to perform a similar training volume for the 3 d before and to avoid vigorous exercise the day before. In addition, they were instructed to maintain a standard mixed diet for 2 d before each trial. Food records were kept before the first trial, and meals were replicated by each subject for the remaining trials. Participants were instructed not to consume alcohol, caffeine, or nonprescription drugs the day before and on the day of a trial. Subjects reported in a normally hydrated condition, accomplished by drinking liberally the day before and drinking one 237-mL glass of water 1 h before the trial. Subjects refrained from exercise for 12 h before testing. They were tested at the same time of day for each trial, which was at least 3 h after a meal. On arrival at the laboratory, subjects completed a 24-h history form to assess compliance with pretest instructions. Experimental-Trial Protocol: Before each trial, subjects drank the first aliquot of the experimental test beverage and completed 100-mm visual analog scales to rate each beverage according to several aspects of taste and gastrointestinal (GI) tolerance. After entering the environmental chamber, subjects sat upright on the cycle ergometer for 10 min to allow plasma volume to stabilize while resting HR was measured. They then ingested the second aliquot of beverage immediately before the start of the cycling test. Subjects cycled for a total of 135 min. The first 120 min were performed at fixed intensities alternating between 60% and 75% VO2max every 15 min using the hyperbolic mode on the ergometer. For the last 15 min, subjects were told to ride as hard as possible (with the ergometer in linear mode), simulating an extended all-out effort at the end of a race. During the ride, HR was measured every 5 min. Statistical Analysis Data from the experimental trials were analyzed using a 3-way (Beverage × Time × Site) mixed-model analysis of variance (beverage and time as repeated measures and site as a between-subjects factor). There were no significant main effects for site or Beverage × Site interaction, indicating that results related to differences among beverages were the same at both test sites. Thus, data from the 2 sites were pooled and are presented as means with standard deviations (SD). Post hoc paired t–tests and simple-effects tests were performed to compare individual mean differences. The Bonferroni alpha-level correction was used to control the family-wise error rate to hold the experiment-wise alpha level at 0.05.
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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) was measured with a Polar Vantage XL monitor (model 145900, Polar Electro, Inc, Woodbury, NY).
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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.) Placebo controls
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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) None
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What conflicts of interest were reported? No information provided
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Refid 17507741
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What were the sources of funding? This research was supported by a grant from The Coca-Cola Company, Atlanta, GA.
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Results & Comparisons

No Results found.