Nitrate & Muscle Performance

Researchers from the University of Exeter Medical school recently published results of a small randomized crossover study, detailing the metabolic fate and physiological significance of supplementation with nitrate, both at rest and before exercise. Participants were randomized to either a stable isotope tracer (K¹⁵NO₃) or placebo, allowing the detection of both nitrate and nitrite in muscle and other tissues, as well as a visualization of the portion supplied by the supplement (vs. endogenously generated nitrate). This study was done in part because of growing evidence that muscle may be a storage depot for nitrate, possibly to provide nitric oxide (NO) to plasma if dietary intake is low.

Within 1 hour of ingestion supplemental nitrate accumulated within muscle tissue, enhancing the total muscle nitrate concentration. Additionally, this increase in muscle nitrate was associated with greater muscle performance, specifically, enhanced peak and mean torque production over the first 1.5 minutes of a “5-minute all out” exercise test, involving intermittent isometric maximal voluntary contractions of the knee extensors. The greater torque was associated with both the pre-exercise levels labeled nitrate as well as the decreased levels of labeled muscle nitrate during exercise. In addition to the apparent increase in exercise performance with supplemental nitrate, it’s also interesting to note that the labeled nitrate accounted for approximately 94%, 96%, and 89% of the total nitrate present in plasma, saliva, and urine, respectively, but only 68% of muscle nitrate, and that although the labeled nitrate in muscle dropped quickly during exercise, the endogenous levels remained the same, suggesting the supplemental form may be at least temporarily more available to muscle tissue than endogenously generated nitrate.