Effects of dietary nitrate, caffeine, and their combination on 20-km cycling time trial performance

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Author
Glaister, Mark
Pattison, John R.
Muniz-Pumares, Daniel
Patterson, Stephen D.
Foley, Paul
Date
2015-01Type
Article
Publisher
National Strength & Conditioning Association
ISSN
1064-8011
Metadata
Show full item recordAbstract
The aim of this study was to examine the acute supplementation effects of dietary nitrate, caffeine, and their combination on 20-km cycling time trial performance. Using a randomized, counterbalanced, double-blind Latin-square design, 14 competitive female cyclists (age: 31 ± 7 years; height: 1.69 ± 0.07 m; body mass: 61.6 ± 6.0 kg) completed four 20-km time trials on a racing bicycle fitted to a turbo trainer. Approximately 2.5 hours before each trial, subjects consumed a 70-ml dose of concentrated beetroot juice containing either 0.45 g of dietary nitrate or with the nitrate content removed (placebo). One hour before each trial, subjects consumed a capsule containing either 5 mg·kg of caffeine or maltodextrin (placebo). There was a significant effect of supplementation on power output (p = 0.001), with post hoc tests revealing higher power outputs in caffeine (205 ± 21 W) vs. nitrate (194 ± 22 W) and placebo (194 ± 25 W) trials only. Caffeine-induced improvements in power output corresponded with significantly higher measures of heart rate (caffeine: 166 ± 12 b·min vs. placebo: 159 ± 15 b·min; p = 0.02), blood lactate (caffeine: 6.54 ± 2.40 mmol·L vs. placebo: 4.50 ± 2.11 mmol·L; p < 0.001), and respiratory exchange ratio (caffeine: 0.95 ± 0.04 vs. placebo: 0.91 ± 0.05; p = 0.03). There were no effects (p ≥ 0.05) of supplementation on cycling cadence, rating of perceived exertion, (Equation is included in full-text article.), or integrated electromyographic activity. The results of this study support the well-established beneficial effects of caffeine supplementation on endurance performance. In contrast, acute supplementation with dietary nitrate seems to have no effect on endurance performance and adds nothing to the benefits afforded by caffeine supplementation.
Journal/conference proceeding
Journal of Strength and Conditioning Research
Citation
Glaister, M., Pattison, J.R., Muniz-Pumares, D., Patterson, S.D. and Foley, P. (2015) 'Effects of dietary nitrate, caffeine, and their combination on 20-km cycling time trial performance', Journal of Strength & Conditioning Research, 29(1), pp. 165-174
Description
Full version published in Journal of Strength and Conditioning Research - available http://dx.doi.org/10.1519/JSC.0000000000000596
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