Arginine is a popular amino acid under athletes because of its supposed ergogenic potential.
Therefore, researchers from the McMaster University in Canada studied if arginine could live up to its reputation.
It has been well established that essential amino acids can stimulate muscle protein synthesis, the building of new muscle tissue.
Arginine is not an essential amino acid, thus has no direct effect on muscle protein synthesis. Yet, arginine is popular under athletes.
The rationale for the use of arginine as ergogenic aid is that it stimulates blood flow via increasing nitric oxide-mediated vasodilation, because arginine is a precursor for NO synthesis.
Theoretically, this would increase nutrient delivery to the muscle. NO is also responsible for the swelling of muscles during exercise, a phenomenon called the pump.
The researchers studied eight subjects who were tested two times:
- once after ingesting a supplement containing 10g of essential amino acids (CON)
- the other time after ingesting a supplement containing 10g of essential amino acids with 10g arginine (ARG)
The essential amino acids where provided because they stimulate muscle protein synthesis. Therefore any increase in blood flow as a result of the arginine would increase amino acid availability to the muscle.
The researchers also wanted to know if the the effect of arginine was different at rest or after exercise. The subjects had to perform leg extensions with one leg. This leg was the exercise group (EX), the resting leg was the control group (CON).
Arginine did not increase blood flow either at rest or after resistance exercise. The effects of arginine on mixed muscle fractional synthesis rate (FSR), a marker of protein synthesis can be seen below
Neither at rest nor after exercise did the addition of arginine to the essential amino acids increase muscle protein synthesis.
These results may seem in conflict with some previous studies. However, earlier work which found positive effects of arginine was done in either a fasting state and/or with intravenous infusion of arginine, which increases the concentration blood concentration of arginine much higher than an oral dose.
The researchers question the ergogenic potential of oral arginine in healthy young man when essential amino acids are provided.