It is a proteinogenic amino acid (i.e. it contributes to the synthesis of new proteins).

Function

  Arginine performs several biological functions that aid post-trainingrecovery. Some of these are exerted directly by the amino acid, while others depend on its ability to stimulate the production of nitric oxide (NO), which then acts on recovery. Prominent among the former functions is its ability to accelerate the disposal of metabolic wastes such as ammonia, produced in large quantities during exertion and, by virtue of this, acting as a remedy for fatigue. As for the functions performed by nitric oxide, the main one is to promote relaxation of the smooth muscles that enclose the blood vessels. Since their constriction hinders the flow of blood and their dilation, on the contrary, promotes it (within certain limits), the action that nitric oxide exerts on the blood vessels is such as to favour blood circulation and, consequently, cell trophism and the disposal of fatigue waste accumulated at peripheral level. Other functions of nitric oxide relate to muscle and tendon recovery. More specifically, it is known that after prolonged physical inactivity, nitric oxide can accelerate muscle recovery; and in the case of tendon damage, nitric oxide inhibition is associated with a delay in tissue regeneration, while its activation can accelerate it.

Negative notes

  If arginine is taken in its pure form, it can often result in intestinal discomfort of a fairly serious nature, especially if taken on an empty stomach. This side effect is less pronounced if it is taken in its hydrochloride form. It also has adverse effects as a stimulator of nitric oxide (currently the most powerful known). Nitric oxide, in fact, also has some destructive effects. More specifically, as nitric oxide is a free oxygen radical, it has a tendency to attack tissues, generating oxidative stress. It is not yet clear why in some circumstances nitric oxide helps protect or survive the cell, while in some others it can kill it. Nitric oxide may also favour the onset of cramps. Lastly, although some studies show nitric oxide’s ability to facilitate β-oxidation (oxidation of fats to produce metabolic energy, which benefits extensive endurance performance and the slimming process), others show, on the contrary, a tendency for it to hinder this process.

Form and posology

  Arginine supplements are mostly commercially available in the form of tablets or powders to be dissolved in a drink. They are available in three different forms: pure arginine, arginine hydrochloride and arginine α-keto-glutarate (alpha-ketoglutarate or AKG). Of the three, the latter is the one that gives rise to the fewest adverse effects (but is also more expensive). Its assimilation is also better. Unfortunately, the bioavailability of arginine, regardless of its form (and as with most amino acids), is very poor. As for dosage, it is known that taking a dose of 0.1g/kg body weight results in a 50% increase in nitric oxide production, while doubling the dosage can quadruple its effectiveness. If, alongside the claims of efficacy, one also considers those of low adverse effects, the advice of Evans (2004) and Collier (2005) is relevant, who suggest that the optimal dose combining benefits and low adverse effects is 9g. If one chooses to take arginine in its hydrochloride form, one should consider that 20 per cent of the product is hydrochloride, so only 80 per cent of the final amount taken will be arginine.