Dietary nitrate supplementation enhances muscle contractile efficiency during knee-extensor exercise in humans

Bailey SJ, Fulford J, Vanhatalo A, Winyard PG, Blackwell JR, DiMenna FJ, Wilkerson DP, Benjamin N, Jones AM. Dietary nitrate supplementation enhances muscle contractile efficiency during knee-extensor exercise in humans. J Appl Physiol 109: 135-148, 2010. First published May 13, 2010; doi:10.1152/japplphysiol.00046.2010.-The purpose of this study was to elucidate the mechanistic bases for the reported reduction in the O-2 cost of exercise following short-term dietary nitrate (NO3-) supplementation. In a randomized, double-blind, crossover study, seven men (aged 19-38 yr) consumed 500 ml/day of either nitrate-rich beetroot juice (BR, 5.1 mmol of NO3-/day) or placebo (PL, with negligible nitrate content) for 6 consecutive days, and completed a series of low-intensity and high-intensity step exercise tests on the last 3 days for the determination of the muscle metabolic (using P-31-MRS) and pulmonary oxygen uptake ((V) over dotO(2)) responses to exercise. On days 4-6, BR resulted in a significant increase in plasma [ nitrite] (mean +/- SE, PL 231 +/- 76 vs. BR 547 +/- 55 nM; P < 0.05). During low-intensity exercise, BR attenuated the reduction in muscle phosphocreatine concentration ([PCr]; PL 8.1 +/- 1.2 vs. BR 5.2 +/- 0.8 mM; P < 0.05) and the increase in (V) over dotO(2) (PL 484 +/- 41 vs. BR 362 +/- 30 ml/min; P < 0.05). During high-intensity exercise, BR reduced the amplitudes of the [ PCr] (PL 3.9 +/- 1.1 vs. BR 1.6 +/- 0.7 mM; P < 0.05) and (V) over dotO(2) (PL 209 +/- 30 vs. BR 100 +/- 26 ml/min; P < 0.05) slow components and improved time to exhaustion (PL 586 +/- 80 vs. BR 734 +/- 109 s; P < 0.01). The total ATP turnover rate was estimated to be less for both low-intensity (PL 296 +/- 58 vs. BR 192 +/- 38 mu M/s; P < 0.05) and high-intensity (PL 607 +/- 65 vs. BR 436 +/- 43 mu M/s; P < 0.05) exercise. Thus the reduced O-2 cost of exercise following dietary NO3- supplementation appears to be due to a reduced ATP cost of muscle force production. The reduced muscle metabolic perturbation with NO3- supplementation allowed high-intensity exercise to be tolerated for a greater period of time.