Effect of Beetroot Juice on Moderate-Intensity Exercise at a Constant Rating of Perceived Exertion

Abstract

Dietary nitrate supplementation has been shown to reduce oxygen consumption at a fixed work rate. We questioned whether a similar effect would be observed during variable work rate exercise at a specific rating of perceived exertion (RPE), as is commonly prescribed for aerobic training sessions. Using a double-blind, placebo controlled, crossover design, ten females (25 ± 3 years; VO₂peak 37.1 ± 5.3 ml/kg/min) performed two 20-min cycle ergometer trials at a constant RPE of 13 (somewhat hard) 2.5 hours following ingestion of 140 ml of concentrated beetroot juice (12.9 mmol nitrate), or nitrate-depleted placebo. Performance was measured in terms of total VO₂ (L) consumed and total mechanical work (kJ) accomplished across each trial. Following each experimental trial, subjects rode at 75W for an additional 5 min to determine the effect of beetroot juice on fixed work rate exercise. Coefficients of variation in total VO₂ (L) and work performed (kJ) during the RPE 13 clamp trials were 8.2 and 9.5%, respectively. Consumption of beetroot juice did not affect total VO₂ or work performed during RPE 13 exercise, but lowered resting systolic blood pressure by ~5 mmHg (P=0.041) and oxygen consumption at 75W by ~4% (P=0.048), relative to placebo. Since the effect of beetroot juice on oxygen consumption is small and may be masked by daily variability during self-regulated exercise, it is unlikely to have a notable effect on daily training.

Keywords: Nitrate; RPE; altitude; nitric oxide; nitrite; reliability.

Figure 1

Individual responses in resting systolic blood pressure 2.5 hours post ingestion of 140ml beetroot juice (12.9 mmol nitrate) or nitrate-free placebo in young, healthy females (n=9). * Beetroot juice reduced average systolic blood pressure by ~5 mmHg (P = 0.041).

Figure 2

Total VO₂ consumed and mechanical work performed over 20 min of exercise at rating of perceived exertion (RPE) of 13 (somewhat hard). Data were collected from young, healthy females (n=9) 2.5 hours post ingestion of 140ml beetroot juice (12.9 mmol nitrate) or nitrate-free placebo in. Beetroot juice did not affect total VO₂ (P = 0.352).

Figure 3

Individual responses in VO₂ (L/min) during exercise at 75W 2.5 hours post ingestion of 140ml beetroot juice (12.9 mmol nitrate) or nitrate-free placebo in young, healthy females (n=9). * Beetroot juice reduced average VO₂ (L/min) by ~4% (P = 0.048).