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Multiple-day high-dose beetroot juice supplementation does not improve pulmonary or muscle deoxygenation kinetics of well-trained cyclists in normoxia and hypoxia

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Torben Rokkedal-Lausch, Jesper Franch, Mathias K. Poulsen, Lars P. Thomsen, Eddie Weitzberg, Ernest N. Kamavuako, Dan S. Karbing, Ryan G. Larsen

Original languageEnglish
Pages (from-to)37-44
Number of pages8
JournalNitric Oxide - Biology and Chemistry
Volume111-112
DOIs
Published1 Jun 2021

Bibliographical note

Funding Information: We would like to thank all the participants for the contribution to the present study. Further, we thank Merete Fredsgaard, Brita Holst Serup, Hanne Krone Nielsen and Ditte Beck Christensen for the support in blood sample collections. We thank Carina Nihlen for support in analyzing blood samples. This study was designed by TRL, JF, RGL, MKP, DSK and LPT; data were collected and analyzed by TRL, JF, RGL, MKP, DSK, LPT, ENK and EW; data interpretation and manuscript preparation were undertaken by TRL, JF, RGL. All authors approved the final version of the paper. Publisher Copyright: © 2021 Elsevier Inc. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

King's Authors

Abstract

Dietary nitrate (NO3) supplementation via beetroot juice (BR) has been reported to lower oxygen cost (i.e., increased exercise efficiency) and speed up oxygen uptake (VO2) kinetics in untrained and moderately trained individuals, particularly during conditions of low oxygen availability (i.e., hypoxia). However, the effects of multiple-day, high dose (12.4 mmol NO3− per day) BR supplementation on exercise efficiency and VO2 kinetics during normoxia and hypoxia in well-trained individuals are not resolved. In a double-blinded, randomized crossover study, 12 well-trained cyclists (66.4 ± 5.3 ml min−1∙kg−1) completed three transitions from rest to moderate-intensity (~70% of gas exchange threshold) cycling in hypoxia and normoxia with supplementation of BR or nitrate-depleted BR as placebo. Continuous measures of VO2 and muscle (vastus lateralis) deoxygenation (ΔHHb, using near-infrared spectroscopy) were acquired during all transitions. Kinetics of VO2 and deoxygenation (ΔHHb) were modeled using mono-exponential functions. Our results showed that BR supplementation did not alter the primary time constant for VO2 or ΔHHb during the transition from rest to moderate-intensity cycling. While BR supplementation lowered the amplitude of the VO2 response (2.1%, p = 0.038), BR did not alter steady state VO2 derived from the fit (p = 0.258), raw VO2 data (p = 0.231), moderate intensity exercise efficiency (p = 0.333) nor steady state ΔHHb (p = 0.224). Altogether, these results demonstrate that multiple-day, high-dose BR supplementation does not alter exercise efficiency or oxygen uptake kinetics during normoxia and hypoxia in well-trained athletes.

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