Study Preview
Study Title and Description
The physiological effects of caffeine in women during treadmill walking.
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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| Title | The physiological effects of caffeine in women during treadmill walking. |
| Author | JN Ahrens,SH Crixell,LK Lloyd,JL Walker, |
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| Year | 2007 |
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Secondary Publication Information
There are currently no secondary publications defined for this study.
Extraction Form: Cardiovascular Design
| Question... Follow Up | Answer | Follow-up Answer | |
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| 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 this study was to determine the acute effects of low and moderate doses of caffeine on heart rate (HR), oxygen consumption (VO2), and perceived exertion (RPE) during treadmill walking in recreationally active women. |
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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 Twenty-six young women (19–28 years of age), enrolled in a personal fitness and wellness aerobic class at a university, volunteered to participate in this study. Three subjects withdrew for personal reasons and 3 withdrew due to adverse reactions to the high caffeine dose (9 mg/kg). [NOTE: Study originally included a dose of 9 mg/kg, but was discontinued due to reported adverse effects.] Results from the 20 remaining subjects were used in the final data analyses. Based on VO2max, the aerobic fitness levels of the participants ranged from poor to good. Based on the 3-day dietary recall, 7 consumed no caffeine, whereas 13 consumed no more than 80 mg of caffeine per day; thus, none of the subjects were considered to be regular users. Therefore, this sample can be generalized to women of varying fitness levels who are not regular users of caffeine. Testing Procedures Subjects visited the laboratory on 4 separate occasions, 2–7 days apart. During visit 1, subjects were measured for height and weight (in exercise clothes, without shoes) using a calibrated physician’s scale (Detecto Scale Co., Jericho, NY), and performed a Bruce graded maximal exercise on a Trackmaster treadmill (FullVision, Newton, KS). During maximal and submaximal exercise tests, each subject’s HR was measured with a Polar Vantage XL telemetric HR monitor (Stanford, CT). Also during their first visit, subjects were instructed to record usual food and beverage intake for 3 days. Before visit 2, their food and beverage records were submitted and were analyzed for nutrient content. Subjects were instructed to replicate their usual intake for the day prior to each remaining trial. In addition, subjects were instructed to prepare for each trial by abstaining from caffeine for 12 hours and eating as they normally would before a bout of exercise, including a light snack 1–2 hours before each trial. Anhydrous caffeine powder (Spectrum Chemicals, New Brunswick, NJ) was measured, was dispensed into capsules, and was placed into coded envelopes by a person who was not involved in data analysis. Placebo capsules were filled with dextrose (Spectrum Chemicals) that had the same color and texture as the caffeine. During visits 2–4, subjects were randomly administered caffeine (3 mg/kg or 6 mg/kg) or placebo with an 8-oz serving of water in a double blind method. After 60 minutes, subjects walked on a Trackmaster treadmill (FullVision) for 8 minutes at 94 m/min (3.5 mph). Statistical Analyses Analyses of variance (ANOVA) with repeated measures were conducted to determine the effect of different doses of caffeine (placebo vs. 3 mg/kg vs. 6 mg/kg) on VO2, HR, rate of energy expenditure (REE), respiratory exchange ration (RER), RPE, and %VO2 max reserve (%VO2R) for the final 3 minutes of each test. When significant differences were observed, post hoc paired t-tests were conducted to determine whether differences in mean values existed between (a) 3 mg/kg of caffeine and the placebo; (b) 6 mg/kg of caffeine and the placebo; or (c) 3 mg/kg and 6 mg/kg of caffeine. The alpha level for each ANOVA was 0.05. The Bonferroni method was used to adjust the alpha level for each post hoc test. |
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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 | HR was measured with a Polar Vantage XL telemetric HR monitor (Stanford, CT). |
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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 | 17313293 |
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| What were the sources of funding? | No information provided |
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Results & Comparisons
No Results found.
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