Beetroot juice ingestion during prolonged moderate-intensity exercise attenuates progressive rise in O2 uptake

Abstract

Nitrate-rich beetroot juice (BR) supplementation has been shown to increase biomarkers of nitric oxide availability with implications for the physiological responses to exercise. We hypothesized that BR supplementation before and during prolonged moderate-intensity exercise would maintain an elevated plasma nitrite concentration ([NO2-]), attenuate the expected progressive increase in VO2 over time, and improve performance in a subsequent time trial (TT). In a double-blind, randomized, crossover design, 12 men completed 2 h of moderate-intensity cycle exercise followed by a 100-kJ TT in three conditions: 1) BR before and 1 h into exercise (BR + BR); 2) BR before and placebo (PL) 1 h into exercise (BR + PL); and 3) PL before and 1 h into exercise (PL + PL). During the 2-h moderate-intensity exercise bout, plasma [NO2+] declined by ∼17% in BR + PL but increased by ∼8% in BR + BR such that, at 2 h, plasma [NO2-] was greater in BR + BR than both BR + PL and PL + PL (P < 0.05).VO2 was not different among conditions over the first 90 min of exercise but was lower at 120 min in BR + BR (1.73 ± 0.24 l/min) compared with BR + PL (1.80 ± 0.21 l/min; P = 0.08) and PL + PL (1.83 ± 0.27 l/min; P < 0.01). The decline in muscle glycogen concentration over the 2-h exercise bout was attenuated in BR + BR (∼28% decline) compared with BR + PL (∼44% decline) and PL + PL (∼44% decline; n = 9, P < 0.05). TT performance was not different among conditions (P > 0.05). BR supplementation before and during prolonged moderate-intensity exercise attenuated the progressive rise in VO2 over time and appeared to reduce muscle glycogen depletion but did not enhance subsequent TT performance. NEW & NOTEWORTHY We show for the first time that ingestion of nitrate during exercise preserves elevated plasma [nitrite] and negates the progressive rise in O2 uptake during prolonged moderateintensity exercise.