Abstract
This study investigated the effects of acute and chronic beetroot juice (BRJ) supplementation on submaximal exercise oxygen uptake (VO 2), time trial (TT) performance, and contractile properties of the plantar flexors in females. Study 1: Using a double blind, randomized, crossover design, 12 recreationally active females using hormonal contraceptives supplemented acutely (2.5 h) and chronically (8 days) with 280 mL BRJ/d (~26 mmoles nitrate [NO3−]) or a NO3−‐free placebo (PLA). On days 1 and 8, participants cycled for 10 min at 50% and 70% VO 2peak and completed a 4 kJ/kg body mass TT. Plasma [NO3−] and nitrite ([NO2 −]) increased significantly following BRJ supplementation versus PLA. There was no effect of BRJ supplementation on VO 2 at 50% or 70% VO 2peak, or TT performance. Study 2: 12 recreationally active females (n = 7 from Study 1) using hormonal contraceptives participated in a baseline visit and were supplemented acutely (2.5 h) and chronically (8 days) with 280 mL BRJ/d. Maximum voluntary strength (MVC) of the plantar flexors was assessed and a torque‐frequency curve performed. BRJ had no effect on MVC, voluntary activation, peak twitch torque, time to peak torque, or half relaxation time. Following both acute (46.6 ± 4.9% of 100 Hz torque) and chronic (47.2 ± 4.4%) supplementation, 10 Hz torque was significantly greater compared to baseline (32.9 ± 2.6%). In summary, BRJ may not be an effective ergogenic aid in recreationally active females as it did not reduce submaximal exercise VO 2 or improve aerobic TT performance despite increasing low frequency torque production.
Highlights
Nitric oxide (NO) is a potent signaling molecule that may play a pivotal role in the regulation of several biological processes including vasodilation (Ignarro et al 1987), mitochondrial efficiency (Larsen et al 2011) and excitation-coupling (Bailey et al 2010; Haider and Folland 2014; Whitfield et al 2016, 2017)
There was no difference in the change in body mass (BM) post-exercise between conditions (Acute PLA, À0.1 Æ 0.5; Chronic PLA, À0.2 Æ 0.3; Acute Beetroot juice (BRJ), À0.2 Æ 0.5; Chronic BRJ, À0.1 Æ 0.3%) indicating that the subjects were adequately hydrated throughout the exercise protocol
Our submaximal exercise economy data demonstrate no effect of BRJ supplementation and are in contrast to other studies in non-elite females (Bond et al 2014; Rienks et al 2015), we believe the data presented in this study provides a strong, well-controlled and comprehensive investigation of acute and chronic BRJ supplementation on exercise economy and time trial (TT) performance in recreationally active females
Summary
Nitric oxide (NO) is a potent signaling molecule that may play a pivotal role in the regulation of several biological processes including vasodilation (Ignarro et al 1987), mitochondrial efficiency (Larsen et al 2011) and excitation-coupling (Bailey et al 2010; Haider and Folland 2014; Whitfield et al 2016, 2017). NO can be generated via two distinct pathways, endogenously through the classic oxygen (O2) dependent L-arginine/NO synthase pathway and exogenously through the O2 independent nitrate (NOÀ3 )-nitrite (NO2À)-NO pathway (Bailey et al 2012). The latter pathway is facilitated by commensal anaerobic bacteria in the oral cavity that sequentially reduce NOÀ3 to NO2À and further to NO (Bailey et al 2012). Beetroot juice (BRJ) has been at the forefront of this research due to its high dietary NOÀ3 content (Hord et al 2009) and has demonstrated effectiveness for general health as well as athletic performance (Bailey et al 2012).
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