Effects of a single dose of beetroot juice on cycling time trial performance at ventilatory thresholds intensity in male triathletes

Abstract

Background

Beetroot juice (BJ) is classified as a high-level supplement for improving sports performance. There is some controversy over the benefits of BJ supplementation for endurance exercise performance, especially when referring to well-trained athletes. This study examines the effects of acute BJ supplementation on cardioventilatory responses, exercise economy/efficiency, slow component of oxygen uptake, time trial performance, blood lactate, energy consumption, and carbohydrate and fat oxidation.

Methods

Twelve well-trained, male triathletes (aged 21–47 yr) were assigned in a randomized, double-blind, crossover design to receive 70 ml of BJ (6.5 mmol NO₃ ⁻) or placebo (PL). Three hours after taking the supplement, participants completed an endurance test on a cycle ergometer at a constant work rate (W) corresponding to first ventilatory threshold (VT1) (30 min) and second ventilatory threshold (VT2) time trial (~ 15 min).

Results

Maximal oxygen uptake was 54.78 ± 3.13 mL·min^− 1·kg^− 1, and gross efficiency was > 22% at each load intensity and experimental condition. No significant interaction effect (supplement*intensity) was observed on any of the cardioventilatory variables, efficiency/economy, VT2 time trial, energy expenditure, carbohydrate oxidation and fat oxidation (p > 0.05).

Conclusion

Our findings do not support an improvement in the variables examined in response to acute BJ supplementation. Probably, higher doses are needed for improving time trial performance in male triathletes during a cycle ergometer test conducted at a load intensity equivalent to the first and second ventilatory threshold.

Keywords:

• Cardioventilatory responses
• Gross mechanical efficiency
• Cycling efficiency
• Slow component
• Energy expenditure

Acknowledgements

The authors would like to thank the triathletes involved in this research for their participation and cooperation.

Availability of data and materials

Data are presented in the manuscript, further information available upon request.

Authors’ contributions

RD, JLM-M and MVG-C conceived and designed the experiments; RD, GP-S, EC, PG-F, AM-G, MCL-E and MVG-C performed the experiments; RD, GP-S, MVG-C, PV-H and JLM-M analyzed the data; AM-G, EC, PG-F, and MCL-E contributed reagents/materials/analysis tools; RD, JLM-M, and MVG-C wrote the paper. All authors read and approved the final manuscript.

Ethics approval and consent to participate

The subjects were informed of the study goals and test protocols before giving their signed informed consent for participation. The study protocol received approval from the Ethics Committee of the Universidad Alfonso X El Sabio (Madrid, Spain) according to the principles and policies of the Declaration of Helsinki.

Consent for publication

Not applicable

Competing interests

The authors declare that they have no competing interests.

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