Muscle-building effect of protein beverages

Many studies recently have been conducting the effects of drinking high protein beverages on enhanced muscle growth; as well as, the effects of amino acid supplements on muscle growth. This specific study, conducted by Stuart Phillips, focused on the amino acid leucine and how it can influence protein synthesis. Furthermore, they focused on the amounts of protein consumed, as well as, the times at which they consumed to determine the effects of that on muscle growth. They broke up participants into groups, one group took shots of protein drink (2.5 g, 10 times) throughout their workouts, another group drank a protein shake after their workout with a low amount of leucine in it (25 g of protein, 1.87 g of leucine), and the last group drank a protein shake after their workout with a high amount of leucine in it (25 g of protein, 3.5 g of leucine). Post exercise muscle protein synthesis was evaluated and it showed that consuming a large amount of protein post exercise increased muscle protein synthesis compared to periodically consuming small doses of protein. Furthermore, the groups that had a higher amount of leucine had a 33% higher muscle protein synthesis compared to the group with the lower amount of leucine in their protein shake. Thus, it as concluded that protein synthesis can be manipulated via dietary action, as well as, it shows that leucine plays an important role in stimulating muscle growth post exercise.

This study shed some light on the role of amino acids and muscle growth. Theoretically, it all makes sense that the more amino acids and protein you consume the more muscle growth you will see (with exercise). However, I was not sure if it necessarily worked that way; my thinking was just because you consume more amino acids does not necessarily mean it will stimulate muscle growth. Furthermore, it does not necessarily mean they will be used, there is still the possibility they will just be excreted. However, it seems these researchers identified a specific amino acid that is directly used for muscle growth after exercise. It would be interesting to see, if there were more amino acids added would there be a greater effect or would it cause the body to excrete the amino acids due to a high amount in the body? Furthermore, does it depend on their genetic background whether or not they would have increased muscle mass due to these supplements?