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

Nitrate-rich beetroot juice (BR) supplementation increases biomarkers of nitric oxide bioavailability 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 𝑉𝑉̇O2 over time, and improve performance in a subsequent time trial (TT). In a double-blind, randomized, crossover design, 12 males 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). 𝑉𝑉̇O2 was not different between conditions over the first 90 min of exercise, but was lower at 120 min in BR+BR (1.73 ± 0.24 L·min-1) compared to BR+PL (1.80 ± 0.21 L·min-1; P=0.08) and PL+PL (1.83 ± 0.27 L·min-1; P<0.01). The decline in muscle [glycogen] over the 2-h exercise bout was attenuated in BR+BR (~28% decline) compared to BR+PL (~44% decline) and PL+PL (~44% decline; n = 9, P<0.05). TT performance was not different between conditions (P>0.05). BR supplementation before and during prolonged moderate-intensity exercise attenuated the progressive rise in 𝑉𝑉̇O2 over time and appeared to reduce muscle glycogen depletion but did not enhance subsequent TT performance.