L-arginine (L-arginine or the salt of L-arginine and Alpha-Ketoglutarate) is a commonly seen amino acid in many pre-work out formulas (including MyProtein’s MyPre and Impact Pump Blend); and as with any substance it is worthwhile investigating its particular benefits to include as single supplement or part of a stack. L-arginine is a conditionally essential amino acid, meaning generally it is produced sufficiently by the body- but occasionally requiring supplementation.
Isolated in 1886 from seeds and animal horn, it was named after the ancient Greek for silver (argiros) due to its silvery white appearance(1,2). This article will investigate whether L-arginine is actually the Silver Bullet for your training worries, and lead you to greater gains.
Where Can I Find L-arginine?
There are a wide variety of food choices (aside from handy supplements) to aid your consumption of this amino acid. The typical dietary intake of this amino acid is 4-5g per day(3).
Animal sources include dairy products (cottage cheese, milk, yogurt); varied meat products (including beef, pork, poultry, game); and sea food (particularly lobster, tuna and halibut).
Plant sources include cereals (granola, oatmeal); various forms of nuts (peanuts, coconut, pecans, walnuts, cashews); seeds; chickpeas; and soya beans.
L-arginine can be synthesised in our bodies from another amino acid, citrulline, in a very energy costly reaction using two specific enzymes (argininosuccinate sythetase and argininosuccinate lyase). However, the synthesis of these enzymes occurs by hydrolysis of ATP to adenosine monphosphate (using ATP which can therefore not be used for energy metabolism).
As such if sufficient L-arginine is consumed; energy (ATP) can be spared for more important metabolic reactions.
What does L-arginine do?
L-arginine is able to assist our physical endeavours in a few different ways- however all of them involve chemical reactions through which L-arginine is used to synthesis different compounds which allow ergogenic benefits.
We will examine these benefits in greater detail.
#1 Nitric Oxide
L-arginine is precursor for the production of nitric oxide (NO). This means it is a necessary compound for a chemical reaction to synthesise NO.
NO is a signalling molecule which has a distinct ability to increase blood flow to muscle tissue. As such increases in NO production should theoretically lead to delivery of essential nutrients and oxygen for metabolism and protein synthesis, whilst simultaneously providing a more efficient waste removal system(4-5).
The process of blood flow improvement is triggered by a cascade of cellular reactions which relax the smooth muscle walls of blood vessels and cause vessel dilation (widening) to facilitate greater blood flow. As such this process would allow greater vessel density (rather than greater volume of blood vessels)(6).
The physical benefits of consuming supplements which trigger NO (not specifically L-arginine) indicate the benefit of sustaining lean body mass whilst reducing body fat (7-9).
In addition to this further animal model experiments indicate that such compounds can also more specifically, acutely initiate thermogenesis (heat production) and increase energy expenditure (10-11).
#2 Growth Hormone
The presence of sufficient L-arginine has also been shown to boost the release of growth hormone (GH) within the body (4, 12-15).
GH is a peptide hormone which works to stimulate growth and regeneration of cells within the body, and is well known for its uses as an anabolic agent in sports and bodybuilding.
In fact L-arginine has been to shown a significantly greater increase in GH levels compared to placebo (3.5µg/L greater) (15).
Interestingly however, in another study the increase of GH seen with 7g of oral L-arginine was not as much as following exercise alone- perhaps indicating that the addition of L-arginine attenuated the GH response.
If GH production is your main objective it is evident that exercise alone is superior to exercise and L-arginine, which in turn is superior to supplementation alone or placebo (16).
Whilst then this may suggest that L-arginine had less potential for use than we expect, if you are to consume on rest days specifically, you are likely to benefit with a boost in GH levels.
L-arginine has been documented to be a substance important in the secretion of not only GH but also various other hormones; including insulin, glucagon, adrenaline and noradrenaline(17-18). It is even suggested to reduce insulin sensitivity(14).
A final biochemical role L-arginine is involved in involves its use as a component in the creatine production in pathway (4-5).
Rather than being an immediate precursor, L-arginine combines with other compounds such as urea, agmatine and ornithine to synthesise creatine.
The physiological benefit of creatine comes from its role in energy production, storage and transfer from the mitochondria to the sites of utilisation in muscle cells (19).
However, as creatine is used, the body requires a continued process of replacement either through diet or endogenous synthesis in the body- hence why this benefit of L-arginine is of interest.
Who can it benefit?
A fantastic study from 2007 evaluated the provision of 3g of L-arginine per day in 20 healthy males(20). They compared this dose to both L-arginine AND vitamin C (1g), and 1g Vitamin C alone (as a control group). They then embarked on an 8 week supplement plan and prescribed a lower limb weight training programme at 70%1RM intensity.
Their results indicated that after 8 weeks the L-arginine group had significantly greater Bodyweight and lean mass, and significantly lower body fat percentage. This was alongside significantly greater leg muscle strength- leading the authors to conclude that oral supplementation of L-arginine (alongside resistance training) enabled strength and mass gains beyond that seen with placebo.
The reasons behind these physiological benefits are proposed to be related to the blood flow efficiency changes secondary to increase in NO- and subsequent decreases in muscle fatigue due to greater glucose uptake (21) and improved contractile function of muscle (22).
A further study (23) supports this theory and showed improvements with resistance to fatigue with a 3g dose of L-arginine over a 15 day period.
Similar results have also been shown to indicate L-arginine supplementation can also boost bench press performance and peak power during a Wingate test (4).
A secondary advantage of utilising the blood flow boosting benefits of L-arginine is facilitation of a greater muscle pump(24).
The haemodynamic changes triggered by supplementation mean an increase in both functional and total blood vessel density(6). This would indicate an acute anaerobic exercise-induced response which alongside appropriate intensity training should have your muscles bursting with blood.
Another effect of L-arginine has been demonstrated influences muscle in a different way. Namely an ability to assist the healing response of muscle injuries.
Animal model studies have shown that strain injuries which damage tissue causing oedema and haemorrhage (when given L-arginine ) will have greater rates of collagen fibre proliferation and angiogenesis compared to controls(25).
This formation of new blood vessels would lead to greater blood flow; and better healing through the transport of nutrients and oxygen and faster removal of waste products.
Another animal model study specifically examined the effect of diets supplemented with L-arginine in aging rats(26).
The results indicate that the negative effects of exhaustive exercise (the release of enzymes which generate free radicals) are attenuated by L-arginine . This reduction in reactive oxygen species mean the aging muscles of the rats will be able to recovery easier and quicker, and there is less chance of overuse pathology.
Interestingly, these benefits are found not only in skeletal muscle but also in myocardial (heart), hepatic (liver), pulmonary (lungs), and renal (kidney tissues).
However, anti oxidant behaviour is not the only heart related benefit of alginine supplementation.
In order to understand the other systemic benefits of L-arginine we have to consider the effect of reduced NO and/ or L-arginine on cardiac function.
For example, essential hypertension (unexplained high blood pressure) is preceded by a disruption in the NO pathway in endothelial tissue(27). This decrease in NO production is in part due to reduced availability and transport of L-arginine (28-29).
Additionally it has been found that 4 weeks of L-arginine supplementation can reduce cardiovascular risk factors (such as systolic blood pressure and intensity of angina symptoms) (30); as well as preventing atherosclerosis (31). These benefits are seen with a dosage of 6g per day in three 2g intervals.
Dosage of L-arginine is somewhat dependent upon a) your current diet (how much L-arginine you already consume) and b) your specific conversion rate to turn L-arginine in to NO (32).
Most studies describe supplementation with a dose of approximately 3g per day to show exercise-induced benefits(20). However, it is worth experimenting with the dose per day and evaluating your response in regards to fatigue, the degree of muscle pump, and of course relative to the state of your current diet.
Safety/Side Effects of L-Arginine
On the basis of the use of L-arginine as an ergogenic or therapeutic supplement experiments have been done on various animal models (rats, pigs, sheep) to assess its safety and toxicity(33).
These experiments indicate that in all animals, whether consumed orally or via IV, L-arginine showed no adverse effects and that the substance is catabolised with 4-5 hours if not utilised. This is the case in animals which are healthy, pregnant, obese or diabetic.
These authors find that doses of 6-15g per day for a 70kg adult, are tolerable for long term consumption, in addition to the regular dietary dose of 4-6g per day.
As such doses of 3g per day for exercise induced benefits are both safe and well tolerated(4).
Take Home Message
It seems that the Silver Bullet of L-arginine supplementation may very well be as beneficial as it is described. Check the labels of your stack and your pre-work out formula and just see if you are getting sufficient amounts of this amino acid, and if not consider an extra dose from a singular L-arginine supplement.
Whether to reduce workout fatigue, boost your muscular pump, or sustain the health of your muscle tissue; L-arginine may be the answer to your supplement needs.