Key result
Dietary nitrate fails to alter primary muscle deoxygenation response time vs placebo but increases end-exercise levels.
Why the study?
The influence of dietary inorganic nitrate supplementation on pulmonary oxygen uptake and muscle deoxygenation kinetics during submaximal cycling exercise was unclear.
Does dietary nitrate supplementation improve pulmonary O2 uptake and muscle deoxygenation kinetics during heavy-intensity cycling in healthy active males?
RCT (n=8)
Placebo-controlled
Randomized
Does dietary nitrate supplementation improve pulmonary O2 uptake and muscle deoxygenation kinetics during heavy-intensity cycling in healthy active males?
p-value: p=> 0.05
Dietary nitrate supplementation increased O2 diffusive conductance across locomotor muscles, which was associated with improved O2 dynamics during heavy-intensity cycling transitions.
Small crossover study links nitrate to greater muscle O2 extraction; leaves open performance or clinical benefits pending larger trials.
This study investigated the influence of dietary inorganic nitrate (NO3−) supplementation on pulmonary O2 uptake (O2) and muscle deoxyhemoglobin/myoglobin (i.e. deoxy [Hb + Mb]) kinetics during submaximal cycling exercise. In a randomized, placebo-controlled, cross-over study, eight healthy and physically active male subjects completed two step cycle tests at a work rate equivalent to 50% of the difference between the gas exchange threshold and peak O2 over separate 4-day supplementation periods with NO3−-rich (BR; providing 8.4 mmol NO3−∙day−1) and NO3−-depleted (placebo; PLA) beetroot juice. Pulmonary O2 was measured breath-by-breath and time-resolved near-infrared spectroscopy was utilized to quantify absolute deoxy [Hb + Mb] and total [Hb + Mb] within the rectus femoris, vastus lateralis, and vastus medialis. There were no significant differences (P > 0.05) in the primary deoxy [Hb + Mb] mean response time or amplitude between the PLA and BR trials at each muscle site. BR significantly increased the mean (three-site) end-exercise deoxy [Hb + Mb] (PLA: 91 ± 9 vs. BR: 95 ± 12 μmol/L, P < 0.05), with a tendency to increase the mean (three-site) area under the curve for total [Hb + Mb] responses (PLA: 3650 ± 1188 vs. BR: 4467 ± 1315 μmol/L sec−1, P = 0.08). The O2 slow component reduction after BR supplementation (PLA: 0.27 ± 0.07 vs. BR: 0.23 ± 0.08 L min−1, P = 0.07) correlated inversely with the mean increases in deoxy [Hb + Mb] and total [Hb + Mb] across the three muscle regions (r2 = 0.62 and 0.66, P < 0.05). Dietary NO3− supplementation increased O2 diffusive conductance across locomotor muscles in association with improved O2 dynamics during heavy-intensity cycling transitions.
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Breese et al. (2017) conducted an RCT in Healthy and physically active (n=8). Dietary inorganic nitrate (NO3-) supplementation (beetroot juice) vs. NO3--depleted (placebo) beetroot juice was evaluated on Primary deoxy [Hb + Mb] mean response time or amplitude (p=> 0.05). Dietary nitrate supplementation did not alter primary deoxy [Hb+Mb] mean response time (P>0.05), but increased mean end-exercise deoxy [Hb+Mb] compared to placebo (95 vs 91 μmol/L; P<0.05).
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