15N‐labeled dietary nitrate supplementation increases human skeletal muscle nitrate concentration and improves muscle torque production
Dietary nitrate (NO3-) supplementation increases nitric oxide bioavailability and can enhance exercise performance. We investigated the distribution and metabolic fate of ingested NO3- at rest and during exercise with a focus on skeletal muscle.
In a randomised, crossover study, ten healthy volunteers consumed 12.8 mmol 15N-labelled potassium nitrate (K15NO3; NIT) or potassium chloride placebo (PLA). Muscle biopsies were taken at baseline, at 1-h and 3-h post-supplement ingestion, and immediately following the completion of 60 maximal intermittent contractions of the knee extensors. Muscle, plasma, saliva and urine samples were analysed using chemiluminescence to determine absolute [NO3-] and [NO2-], and by mass spectrometry to determine the proportion of NO3- and NO2- that was 15N-labelled.
Neither muscle [NO3-] nor [NO2-] were altered by PLA. Following NIT, muscle [NO3-] (but not [NO2-]) was elevated at 1-h (from ~35 to 147 nmol.g-1, P<0.001) and 3-h, with almost all of the increase being 15N-labelled. There was a significant reduction in 15N-labelled muscle [NO3-] from pre- to post-exercise. Relative to PLA, mean muscle torque production was ~7% greater during the first 18 contractions following NIT. This improvement in torque was correlated with the pre-exercise 15N-labelled muscle [NO3-] and the magnitude of decline in 15N-labelled muscle [NO3-] during exercise (r=0.66 and r=0.62, respectively; P<0.01).
This study shows, for the first time, that skeletal muscle rapidly takes up dietary NO3-, the elevated muscle [NO3-] following NO3- ingestion declines during exercise, and muscle NO3- dynamics are associated with enhanced torque production during maximal intermittent muscle contractions.
University of Exeter
University of Queensland
- Sport, Exercise and Health Sciences