Beetroot Juice Does Not Enhance Supramaximal Intermittent Exercise Performance in Elite Endurance Athletes

Abstract

Objective: Nitrate (NO₃⁻)-rich beetroot juice (BR) is recognized as an ergogenic supplement that improves exercise tolerance during submaximal to maximal intensity exercise in recreational and competitive athletes. A recent study has investigated the effectiveness of BR on exercise performance during supramaximal intensity intermittent exercise (SIE) in Olympic-level track cyclists, but studies conducted in elite endurance athletes are scarce. The present study aimed to determine whether BR supplementation enhances the tolerance to SIE in elite endurance athletes.

Methods: Eleven elite endurance athletes (age: 21.7 ± 3.7 years, maximal oxygen uptake $\left({\dot{\mathrm{V}}\mathrm{O}}_{2\mathrm{m}\mathrm{ax}}\right):$ 71.1 ± 5.2 mL·kg⁻¹·min⁻¹) performed an SIE test until exhaustion following either a 3-day BR supplementation (340 mg/d) or a placebo (PL) supplementation (<2.5 mg/d) in a randomized, single blind, placebo-controlled, and crossover study. The exercise test consisted of 15-second cycling exercise bouts at 170% of the maximal aerobic power interspersed with 30-second passive recovery periods. Gas exchange was measured during SIE tests as local muscle O₂ delivery and extraction were assessed by near infrared spectroscopy.

Results: The number of repetitions completed was not significantly different between BR (13.9 ± 4.0 reps) and PL conditions (14.2 ± 4.5 reps). BR supplementation did not affect oxygen uptake (${\dot{\mathrm{V}}\mathrm{O}}_2$) during SIE tests (BR: 3378.5 ± 681.8 mL·min⁻¹, PL: 3466.1 ± 505.3 mL·min⁻¹). No significant change in the areas under curves was found for local muscle total hemoglobin (BR: 6816.9 ± 1463.1 arbitrary units (a.u.), PL: 6771.5 ± 3004.5 a.u.) and deoxygenated hemoglobin (BR: 6619.7 ± 875.8 a.u., PL: 6332.7 ± 1336.8 a.u.) during time-matched work + recovery periods from SIE tests following BR supplementation.

Conclusions: BR supplementation does not enhance the tolerance to SIE in elite endurance athletes and affects neither ${\dot{\mathrm{V}}\mathrm{O}}_2$ nor local muscle O₂ delivery and extraction.

Keywords:

• Dietary nitrate
• high aerobic fitness
• exercise tolerance
• endurance athletes
• intermittent exercise

Acknowledgements

We are grateful to the athletes who took part to the study. We thank the nurses at the Haute Ecole Provinciale du Hainaut (Tournai, Belgium) for their assistance during the experimental protocol.

Authors J.A., J.B., S.B., and M.P.-C. conceived and designed the research; authors J.A., J.B., F.-X.G., D.M., G.C., and M.P.-C. conducted the research; authors J.A., J.B., D.M., and M.P.-C. analyzed the data or performed statistical analysis; authors J.A., J.B., F.-X.G., G.C., D.M., S.B., and M.P.-C. wrote the article. M.P.-C. and J.A. had primary responsibility for final content. All authors read and approved the final manuscript.

Disclosure Statement

The authors do not have any conflicts of interest to disclose. No funding was received for this study.