Introduction: Beetroot juice (BRJ) is a nutritional supplement that has received widespread attention over the last decade. Dietary nitrate (NO₃⁻) reduces the oxygen cost of submaximal exercise and improves performance in recreationally active males both acutely and chronically. The ergogenic effects of BRJ have been attributed to its high nitrate content. However, the evidence supporting the effects of BRJ in females is lacking.

Purpose: To investigate the effects of acute and chronic BRJ supplementation on submaximal exercise oxygen uptake (VO₂) and time trial performance (~30 min) in recreationally active females.

Methods: Using a double-blind, randomized, crossover design, 12 recreationally active females who were taking oral contraceptives supplemented acutely (2.5 hr) and chronically (8 days) with 280 mL BRJ/day (~26 mmoles NO₃⁻) or the same volume of a nitrate-free BRJ (PLA). All trials were conducted at the same time in the morning, and there was a 9 ± 0.7 day washout period between trials. Subjects arrived to the laboratory, a baseline blood sample was drawn, a standardized breakfast including 140 mL BRJ or PLA was provided, and a second blood sample was drawn 2 hr later. Blood samples were analyzed for plasma NO₃⁻ and nitrite (NO₂⁻), as well as estrogen and progesterone. The subjects then cycled for 10 min at 50% and 10 min at 70% VO_2peak, and completed a 4 kJ/kg body mass time trial (TT). Ratings of perceived exertion (RPE), heart rate (HR) and revolutions per minute (rpm) were recorded at 5 min intervals during the submaximal cycling protocol. RPE, HR, rpm, and power output (PO) were recorded as the subjects completed each 20% of the TT.

Results: There were no significant differences in estrogen or progesterone levels between trials. Plasma NO₃⁻ concentrations increased significantly following BRJ supplementation compared to PLA (Acute PLA: 44 ± 3 and Chronic PLA, 41 ± 3 μM vs. Acute BRJ, 761 ± 31 and Chronic BRJ, 1091 ± 58 μM). Similarly, plasma NO₂⁻ increased significantly following BRJ supplementation compared to PLA (Acute PLA, 265 ± 25 and Chronic PLA, 278 ± 26 nM vs. Acute BRJ, 753 ± 84 and Chronic BRJ, 729 ± 101 nM). There was no significant difference in mean VO₂ at 50% VO_2peak (Acute PLA, 1254 ± 45: Acute BRJ, 1259 ± 46: Chronic PLA, 1267 ± 45: Chronic BRJ, 1252 ± 42 mL/min O₂) and 70% VO_2peak (Acute PLA, 1804 ± 60: Acute BRJ, 1791 ± 53: Chronic PLA, 1814 ± 54: Chronic BRJ, 1789 ± 54 mL/min O₂) between trials. No significant difference was found for rpm, HR, or RPE at 50% or 70% VO_2peak. TT performance was unaffected by BRJ (Acute PLA, 1709 ± 75: Acute BRJ, 1813 ± 97: Chronic PLA, 1751 ± 78: Chronic BRJ, 1791 ± 102 s). No significant difference was found for HR, RPE, or PO between conditions throughout the time trial.

Conclusion: BRJ did not reduce submaximal exercise oxygen uptake or improve aerobic TT performance in recreationally active females. Future studies should investigate the potential sex differences that may exist with respect to the ergogenic effects of BRJ supplementation.