The thing about collagen is that like any other orally ingested protein, it is digested into small peptides and amino acids, with a preponderance of glycine, proline, and hydroxyproline. These are small components of muscle proteins ( myosin and actin). Digested and absorbed amino acids and small peptides contribute to the pool of amino acids that is used throughout the body. So getting protein from a variety of sources seems like the best approach.