Plasma nitrate (NO) and nitrite (NO) increase in a dose-dependent manner following NOingestion. To explore if the same dose-response relationship applies to other nitric oxide (NO) congeners in different blood compartments and skeletal muscle, as well as the subsequent physiological responses, we provided 11 healthy participants with NOdepleted beetroot juice (placebo), and beetroot juice (BR) containing 6.4, 12.8 and 19.2 mmol NOin a randomised, crossover design. Blood and muscle samples were collected, and resting blood pressure (BP) was assessed, before and at 2.5-3 h post-ingestion. Muscle contractile function was assessed using a 5-min all-out maximal voluntary isometric knee extension test at 3.5 h post-ingestion. We found that plasma and skeletal muscle [NO], and whole blood S-nitrosothiols ([RSNOs]) increased dose-dependently, while plasma [NO] did not increase further with doses above 6.4 mmol NO. No significant increases in skeletal muscle [NO] were found following ingestion of any of these doses. Resting BP was only reduced after ingestion of 19.2 mmol NO. Mean peak torque and mean torque impulse during the first 10 muscle contractions were significantly enhanced following ingestion of both 12.8 mmol and 19.2 mmol NOcompared to placebo, while the mean absolute rate of torque development (RTD) at 0-50 ms and 0-100 ms was significantly improved following ingestion of 6.4 mmol NOcompared to placebo and 19.2 mmol NO. Significant correlations were found between changes in red blood cell [RSNOs] and changes in absolute RTD at 0-50 ms (r = -0.70, P = 0.02) and 0-100 ms (r = -0.84, P < 0.01) following the ingestion of 6.4 mmol NO. Our findings suggest that a high dose of 12.8 mmol NOis necessary to improve muscle contractile torque, while a lower dose of 6.4 mmol NOis sufficient to enhance muscle contractile velocity, at least for the type of exercise employed in the present study. 3 2 3 3 3 3 2 3 2 3 3 3 3s s3 3 3 ----------------
