Effects of beetroot juice supplementation on cycling performance in normoxic and hypoxic conditions

Authors

Averi Firari, James Madison UniversityFollow

Creative Commons License

This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.

Date of Graduation

5-11-2023

Semester of Graduation

Spring

Degree Name

Master of Science (MS)

Department

Department of Kinesiology

Second Advisor

Nicholas Luden

Third Advisor

Stephanie Kurti-Luden

Abstract

Purpose: The purpose of this study was to examine the effects of dietary nitrate supplementation on physiological responses and cycling performance in recreationally trained (RT; VO_2max = 44 ± 7 ml/kg/min), and highly trained (HT; VO_2max = 66 ± 5 ml/kg/min) cyclists in both normoxic (NO; 20.9% FiO2) and hypoxic (HYP; 15.2% FiO2) conditions. Methods: 13 cyclists completed 4 exercise trials over the course of 4 weeks. For 3 days prior to each trial, subjects consumed 12.8 mmol of supplemental nitrates [from 140mL/d of concentrated beetroot juice (BRJ)] or placebo (PLA; 140mL/d de-nitrated beetroot juice). Subjects completed trials for both treatments (PLA or BRJ) in both environmental conditions (NORM or HYP), in a randomly counterbalanced, double-blinded study design. Expired nitric oxide (eNO), and blood pressure were assessed prior to exercise, both before and 2.5 h following consumption of the final supplement. Exercise trials consisted of 20 min of constant-load cycling, including 10 min at 45% W_max and 10 min at 65% W_max. Immediately following constant-load exercise, participants completed a 4 km cycling time trial (TT). Physiological responses to exercise (including VO₂, ventilation, RER, heart rate, RPE, blood glucose/lactate, and O₂ saturation) were obtained 5 min into constant-load exercise at each intensity. Performance was assessed as the time to complete the 4 km TT with a maximal effort. Treatment effects were assessed using a series of two-way repeated measures ANOVAs [within-subject factors: treatment (BRJ vs PLA), environment (HYP vs NORM); between-subject factor: training group (RT vs HT)], with a levels for statistical significance set at p < 0.05. Results: eNO was significantly higher following BRJ supplementation versus PLA. No treatment effects were observed on systolic or diastolic blood pressure. The HT group (384 ± 16 s) had significantly faster 4 km times than RT (446 ± 42 s), and significant between-group effects were observed for various physiological responses during constant-load exercise (VO₂, ventilation, blood lactate, heart rate, and O₂ saturation). Similarly, TT times were significantly faster in NORM (410 ± 46 s) versus HYP (434 ± 45 s), with significantly different physiological values observed between environmental conditions during constant-load exercise (VO₂, ventilation, RER, blood lactate, heart rate, O₂ saturation, and RPE). However, there was no difference in TT performance between PL (422 ± 44 s) and BRJ treatments (422 ± 46 s), and no significant treatment*altitude or treatment*altitude*group interactions for TT performance or any physiological variables. Conclusion: Dietary nitrate supplementation did not alter physiological responses during exercise, or 4 km TT performance in cyclists. Furthermore, the efficacy of dietary nitrate supplementation was not affected by hypoxic conditions or the training status of subjects.