No effect of beetroot juice supplementation on exercise economy and performance in recreationally active females despite increased torque production

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.

Ergogenic Effect of Nitrate Supplementation: A Systematic Review and Meta-analysis

“…3 A). As has been suggested by Wickham and colleagues ( 112 ) in a recent investigation and review ( 23 ), women are heavily underrepresented in this field of research as is generally observed in biomedical research ( 116 ). Six studies that examined women only or presented data separately for women found no effect of NO 3 − supplementation on exercise performance ( P = 0.347).…”

The Effect of Dietary Nitrate Supplementation on Isokinetic Torque in Adults: A Systematic Review and Meta-Analysis

“…In addition to isokinetic torque, the effect of NO 3 − supplementation on different aspects of skeletal muscle contractile function is equivocal. Indeed, NO 3 − supplementation has been reported to increase force production at low stimulation frequencies in some (≤20 Hz) [ 22 , 23 , 24 ] but not all studies [ 25 , 26 ]. Although most studies have not observed an increase in maximal voluntary isometric contractile force after dietary NO 3 − supplementation [ 19 , 22 , 23 , 25 , 26 , 28 , 29 ], improved weightlifting performance [ 30 , 31 , 32 , 48 , 60 ] and concentric and eccentric contractile force during the back squat [ 61 ] have been reported after dietary NO 3 − supplementation.…”

“…The effect of NO 3 − supplementation on involuntary electrically evoked contractions is equivocal. NO 3 − supplementation has been reported to increase force production at low stimulation frequencies in some (≤20 Hz) [ 22 , 23 , 24 ], but not all studies [ 25 , 26 ]. Although dietary NO 3 − supplementation has been reported to improve maximal voluntary contractile force during a mid-thigh pull [ 27 ], most studies have not observed an increase in maximal voluntary isometric contractile force when contracting the knee extensors [ 19 , 22 , 23 , 25 , 26 , 28 , 29 ].…”

No longer beeting around the bush: a review of potential sex differences with dietary nitrate supplementation

“…Most of this work has been performed using male subjects. However, recent work from our laboratory demonstrated an improvement in skeletal muscle torque production following both acute and chronic dietary NO 3 supplementation in recreationally active females (Wickham et al 2019). This suggests that dietary NO 3 can influence skeletal muscle contractile properties in both sexes; however, the changes may not be large enough to translate into whole-body reductions in V O 2 or increases in performance in recreationally active females.…”

“…There was no effect of BRJ on the work completed or total V O 2 . However, V O 2 was reduced by 4% during a 5-min cooldown where the subjects cycled for 5 min at 75 W. A recent study by Wickham et al (2019) examined the effects of acute and chronic BRJ supplementation on submaximal cycling V O 2 and TT performance in 12 recreationally active females using hormonal contraceptives. The subjects supplemented acutely (2.5 h prior) and chronically (8 days) with 280 mL BRJ/day (ϳ26 mmol NO 3 -) or a NO 3 --free PL.…”