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

Author

Averi Firari, James Madison UniversityFollow

Creative Commons License

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

Date of Graduation

5-11-2023

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Department of Graduate Kinesiology

Advisor(s)

Michael Saunders

Nicholas Luden

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.

Recommended Citation

Firari, Averi, "Effects of beetroot juice supplementation on cycling performance in normoxic and hypoxic conditions" (2023). Masters Theses, 2020-current. 207.
https://commons.lib.jmu.edu/masters202029/207