Resumen de The effect of nitric oxide donors on human performance
Nitric oxide or nitrogen monoxide (NO) is a tiny free radical gas which was initially termed endothelium-derived relaxing factor (EDRF).Currently, it is known that NO plays an important role in the bodies of all mammals. In the circulation system it has vasodilatory and anti-aggregatory properties. For his propierties, it has been hypothesized that dietary compounds related to NO such as L-arginine and inorganic nitrate are ergogenic aids. This claim is based on the potential effects on regulation of blood flow and mitochondrial respiration of NO during physical exercise. It has been suggested that the increased blood flow derived from dietary NO donors such as L-arginine or nitrate may improve blood delivery and substrates of the activated tissues. This physiological response can enhance muscle work capacity and exercise performance. In addition, an increase in the overall workload stimulates stress on exercised muscle tissues, resulting in muscle hypertrophy of the activated muscles. These supposed benefits have been claimed in many sport supplements which are currently sold on the market and linked with stimulation of NO production. However, there is a lack of evidence analyzing this supposed effects. For this reason the aim of this thesis was to investigate the effect of nitric oxide donors on human performance. This thesis is supported by four manuscripts and the main conclusions of this works were: ¿ Dietary L-arginine supplementation at different doses does not increase plasma NO metabolites in competitive tennis players. ¿ Higher doses of dietary L-arginine does not alter the cardiorespiratory and metabolic response to endurance exercise in trained athletes. ¿ Acute as well as 3 days of dietary inorganic nitrate supplementation significantly increase blood levels of nitrate in endurance-trained athletes. ¿ Inorganic dietary nitrate does not induce an increase in plasma levels of nitrite in all endurance-trained athletes. ¿ Gross Efficiency, defined as the ratio of mechanical work output to the metabolic energy input, is not improved by acute ingestion of inorganic nitrate in well-trained athletes. ¿ Maximal oxygen uptake during maximal exercise is significantly reduced after ingestion of one dose of nitrate. This physiological response does not alter performance measured as time-to-exhaustion during an incremental test. ¿ Three days of inorganic nitrate supplementation does not enhance overall performance measured as mean power output and total distance during a 40-min time trial in trained subjects. ¿ Plasma endothelin-1 levels in the forearms are significantly increased after dietary nitrate supplementation just after a 40-min time trial test. ¿ Current scientific data indicates that NO donors have no effect on increasing exercise performance in well-trained athletes. ¿ The benefits reported in some studies analyzing L-arginine and L-citrulline supplementation could be derived from the other ingredients included in supplements as well as from other metabolic pathways, independently of NO synthesis, which these amino acids participate in.
