Oral injection of amino acids is effective
Oral injection of amino acids is effective

Postexercise net protein synthesis in human muscle from orally administered amino acids


Researchers previously found that intravenous infusion of amino acids decreased muscle protein breakdown and increased muscle protein synthesis when given after a bout of resistance exercise. Prior to this study, however, it was unclear whether amino acids taken orally would have the same anabolic effects. It also was unclear if consumption of nonessential amino acids is required for the stimulation of muscle anabolism.

Trial Length

Acute metabolic study

Number of Subjects



All genders

Age Range


The Goal

The present study examined the effects of oral amino acid ingestion on muscle protein metabolism after resistance exercise. A second goal was to assess whether nonessential amino acids are a necessary component of a muscle-building supplement. 

The Results

Participants received a placebo solution (PLA), 40 grams of mixed amino acids (MAA), and 40 grams of just essential amino acids (EAA) on three separate occasions 2 weeks apart.

Results showed that oral administration of both mixed amino acids and essential amino acids boosted net muscle protein balance. See Figure 1 below.

Since the anabolic effect was similar for MAA and EAA, researchers concluded that nonessential amino acids are unnecessary for increasing muscle protein synthesis after resistance exercise.


Researchers determined that supplementing with essential amino acids orally results in a positive net protein balance similar to that produced by intravenous administration of amino acids, and that nonessential amino acids are unnecessary in a supplement designed to stimulate muscle anabolism after resistance exercise. 

The Why?

Both muscle protein synthesis and muscle protein breakdown are increased after exercise. Athletes, fitness enthusiasts, and individuals undergoing physical rehabilitation could benefit from a positive net protein balance. Intravenous infusion of amino acids has been proven to increase muscle protein anabolism, however, this delivery method is impractical as a daily supplementation regimen. This research points to the muscle-stimulating effects of taking amino acids orally, a far more convenient and preferable delivery method.


Tipton KD, Ferrando AA, Phillips SM, Doyle D Jr, Wolfe RR. Postexercise net protein synthesis in human muscle from orally administered amino acids. Am J Physiol. 1999;276(4):E628-E634. doi:10.1152/ajpendo.1999.276.4.E628