Muscle tissue is broken down during exercise. It's built back bigger and stronger with rest and amino acids from protein. Research published in the journal Nutrition & Metabolism points out some interesting facts about this process in which muscle protein synthesis plays a crucial role.
Amino acids from protein can elevate levels of protein synthesis for only a few hours, but the effect is optimized when protein is consumed immediately after exercise. This strategic timing can increase baseline rates of protein synthesis by 100% to 150%. The Essential Amino Acids appear to be the best choice for stimulating protein synthesis, with Leucine from the subgroup known as Branched Chain Amino Acids (BCCAs) standing out as the single best trigger.
Your next question is bound to be, "what's the best protein source for Leucine?" According to another study appearing in the same journal, the Leucine concentration of wheat protein is 6.8% and for soy it's 8%. The Leucine concentration of egg protein is 8.8% and it's 10.9% in whey, which is also a rich source for the other two BCAAs Isoleucine and Valine. Use this knowledge to your advantage during recovery.