Protein and amino acid requirements are established using a method known as indicator amino acid oxidation. To find out the amount of amino acids needed to maximize whole body protein synthesis after endurance exercise, researchers applied this tool to lab rats. Findings were published in The Journal of Nutrition.
After dividing the rodents into trained and untrained groups, researchers had their 4-legged subjects run a treadmill for an hour 5 days a week for 6 weeks. Immediately after running, the optimal amino acid intake for trained rats was 26.8 grams per kilogram of body weight.
Inactive rats only needed 15 grams of amino acids per kg of body weight to maximize protein synthesis, and trained rats at rest could get by with 13.3 grams. Humans aren’t rats, of course. What this research suggests is exercise increases your need for amino acids.