No Effect of Acute Beetroot Juice Supplementation on Moderate and Vigorous Intensity Aerobic Exercise

Abstract

Nitric oxide (NO) plays a critical role in regulating blood flow to skeletal muscle. NO production in humans is 1) oxygen-dependent via NO-synthases that convert L-arginine to NO and 2) oxygen-independent via the nitrate-nitrite-NO pathway. The latter pathway is largely dependent on the intake of nitrate-rich foods, such as beetroot and beetroot juice supplements (BR). Consumption of BR has been shown to lower resting blood pressure and the volume of oxygen (VO2) required to perform submaximal aerobic exercise. PURPOSE: The purpose of the present study was to investigate the acute effect of a low dose of BR compared to placebo (PL) during moderate and vigorous intensity aerobic exercise. METHODS: Ten female division-3 collegiate club-level volleyball players (mean ± SD: age = 19.3 ± 1.3 yr, VO2peak = 37.4 ± 3.3 ml·kg-1·min-1) completed three exercise trials consisting of an initial graded test to exhaustion and two performance trials on a motorized treadmill. For the performance trials, participants consumed either 60 mL of BR or PL, three hours prior to five minutes of walking/jogging at 45%, 65%, and 85% of volume of oxygen uptake reserve (VO2R). RESULTS: Separate two-way repeated measures ANOVAs were run to determine the effect of treatment (BR or PL) and exercise intensity (45%, 65%, and 85% VO2R) on VO2, heart rate (HR), and rating of perceived exertion (RPE). Paired samples t-tests were run to compare differences between resting systolic (SBP) and diastolic blood pressure (DBP) between treatments. All data are reported mean ± standard deviation with statistical significance accepted at p < 0.05. There were no statistically significant interactions between treatment and exercise intensity for VO2, HR, or RPE. The main effect of treatment was not statistically significantly different for VO2 (BR: 19.9 ± 6.6 vs. PL: 20.4 ± 6.5 ml·kg-1·min-1; p = .360), HR (BR: 131.3 ± 25.8 vs. PL: 135.4 ± 25.3 beats·min-1; p = .172), or RPE (BR: 9.8 ± 2.2 vs. PL: 9.9 ± 2.4; p = .504). There were no statistically significant differences in resting SBP (BR: 110.6 ± 6.8 vs. PL: 112.7 ± 8.0; p = .166) or DBP (BR: 70.8 ± 5.5 vs. PL: 73.3 ± 6.6; p = .275) between treatments. CONCLUSIONS: These results suggest that a low dose of BR taken three hours prior to moderate and vigorous intensity aerobic exercise has no effect on VO2, HR, RPE, or resting SBP and DBP.