Synergetic Effect of NO Precursor Supplementation and Exercise Training.

INTRODUCTION: Nitric oxide (NO) precursor supplementation has been shown to increase NO bioavailability and can potentially improve vascular function and exercise performance. It remains unclear whether the combination of NO precursor supplementation and exercise training has synergic effects on exercise performance. This study aims to assess the effect of chronic nitrate and citrulline intake on exercise training adaptations in healthy young individuals. METHODS: In this randomized, double-bind trial, 24 healthy young (12 females) subjects performed vascular function assessment (blood pressure, pulse wave velocity, postischemia vasodilation, and cerebrovascular reactivity) and both local (submaximal isometric unilateral knee extension) and whole-body (incremental cycling) exercise tests to exhaustion before and after a 2-month exercise training program and daily intake of a placebo or a nitrate-rich salad and citrulline (N + C, 520 mg nitrate and 6 g citrulline) drink. Prefrontal cortex and quadriceps oxygenation was monitored continuously during exercise by near-infrared spectroscopy. RESULTS: N + C supplementation had no effect on vascular function and muscle and cerebral oxygenation during both local and whole-body exercise. N + C supplementation induced a significantly larger increase in maximal knee extensor strength (+5.1 ± 3.5 vs +0.2 ± 5.5 kg, P = 0.008) as well as a trend toward a larger increase in knee extensor endurance (+35.2 ± 26.1 vs +24.0 ± 10.4 contractions, P = 0.092) than placebo, but no effect on exercise training-induced maximal aerobic performance improvement. CONCLUSION: These results suggest that chronic nitrate and citrulline supplementation enhances the effect of exercise training on quadriceps muscle function in healthy active young individuals, but this does not translate into improved maximal aerobic performances.

Effect of chronic nitrate and citrulline supplementation on vascular function and exercise performance in older individuals.

Increased nitric oxide (NO) bioavailability may improve exercise performance and vascular function. It remains unclear whether older adults who experience a decreased NO bioavailability may benefit from chronic NO precursor supplementation. This randomised, double-blind, trial aims to assess the effect of chronic NO precursor intake on vascular function and exercise performance in older adults (60-70 years old). Twenty-four healthy older adults (12 females) performed vascular function assessment and both local (knee extensions) and whole-body (incremental cycling) exercise tests to exhaustion before and after one month of daily intake of a placebo (PLA) or a nitrate-rich salad and citrulline (N+C, 520mg nitrate and 6g citrulline) drink. Arterial blood pressure (BP) and stiffness, post-ischemic, hypercapnic and hypoxic vascular responses were evaluated. Prefrontal cortex and quadriceps oxygenation was monitored by near-infrared spectroscopy. N+C supplementation reduced mean BP (-3.3mmHg; p=0.047) without altering other parameters of vascular function and oxygenation kinetics. N+C supplementation reduced heart rate and oxygen consumption during submaximal cycling and increased maximal power output by 5.2% (p<0.05), but had no effect on knee extension exercise performance. These results suggest that chronic NO precursor supplementation in healthy older individuals can reduce resting BP and increase cycling performance by improving cardiorespiratory responses.

Effects of acute nitric oxide precursor intake on peripheral and central fatigue during knee extensions in healthy men.

NEW FINDINGS: What is the central question of this study? What is the effect of acute NO precursor intake on vascular function, muscle and cerebral oxygenation and peripheral and central neuromuscular fatigue during knee-extension exercise? What is the main finding and its importance? Acute NO precursor ingestion increases the plasma concentrations of NO precursors (nitrate, arginine and citrulline) and enhances post-ischaemic vasodilatation, but has no significant effect on muscle and cerebral oxygenation, peripheral and central mechanisms of neuromuscular fatigue and, consequently, does not improve exercise performance. ABSTRACT: Nitric oxide (NO) plays an important role in matching blood flow to oxygen demand in the brain and contracting muscles during exercise. Previous studies have shown that increasing NO bioavailability can improve muscle function. The aim of this study was to assess the effect of acute NO precursor intake on muscle and cerebral oxygenation and on peripheral and central neuromuscular fatigue during exercise. In four experimental sessions, 15 healthy men performed a thigh ischaemia-reperfusion test followed by submaximal isometric knee extensions (5 s on-4 s off; 45% of maximal voluntary contraction) until task failure. In each session, subjects drank a nitrate-rich beetroot juice containing 520 mg nitrate (N), N and citrulline (6 g; N+C), N and arginine (6 g; N+A) or a placebo (PLA). Prefrontal cortex and quadriceps near-infrared spectroscopy parameters were monitored continuously. Transcranial magnetic stimulation and femoral nerve electrical stimulation were used to assess central and peripheral determinants of fatigue. The post-ischaemic increase in thigh blood total haemoglobin concentration was larger in N (10.1 ± 3.7 mmol) and N+C (10.9 ± 3.3 mmol) compared with PLA (8.2 ± 2.7 mmol; P < 0.05). Nitric oxide precursors had no significant effect on muscle and cerebral oxygenation or on peripheral and central mechanisms of neuromuscular fatigue during exercise. The total number of knee extensions did not differ between sessions (N, 71.9 ± 33.2; N+A, 73.3 ± 39.4; N+C, 74.6 ± 34.0; PLA, 71.8 ± 39.9; P > 0.05). In contrast to the post-ischaemic hyperaemic response, NO bioavailability in healthy subjects might not be the limiting factor for tissue perfusion and oxygenation during submaximal knee extensions to task failure.

Effect of acute nitrate and citrulline supplementation on muscle microvascular response to ischemia-reperfusion in healthy humans.

Nitric oxide (NO) is implicated in vasomotor control mechanisms altering the diameter of the vessels under various physiological and pathological conditions. There are 2 main NO production pathways, 1 NO synthase (NOS) independent (nitrate-nitrite-NO) and the other is NOS dependent (citrulline-arginine-NO). The objective of the study was to evaluate the effect of acute nitrate and citrulline supplementation on post-ischemic vascular response in healthy subjects. Fourteen subjects performed 2-leg vascular occlusion tests, 3 days apart. They were randomly assigned to consume a drink containing 1200 mg (19.4 mmol) of nitrate and 6 g of citrulline (N+C) or a placebo (Pl). Changes in total hemoglobin (Hbtot) and oxyhemoglobin (HbO2) concentrations were recorded by near-infrared spectroscopy on the thigh and calf muscles. No differences between N+C and Pl were observed during the ischemic period. Hbtot increased to a larger extent during the reperfusion period for the thigh (e.g., area under the curve, 821 ± 324 vs. 627 ± 381 mmol·s-1, p = 0.003) and the calf (515 ± 285 vs. 400 ± 275 mmol·s-1, p = 0.029) in the N+C versus Pl conditions. Similar results were found regarding HbO2 for the thigh (e.g., area under the curve, 842 ± 502 vs. 770 ± 491 mmol·s-1, p = 0.077) and the calf (968 ± 536 vs. 865 ± 275 mmol·s-1, p = 0.075). The larger postocclusive Hbtot and HbO2 responses observed after N+C intake suggests a greater post-ischemic vasodilation, which may be due to increased NO availability, via the activation of the 2 main NO production pathways.