Peptides are short chains of amino acid monomers linked by peptide bonds. They have many functions in the body. Some act like neurotransmitters, others like hormones. There are several amino acids that are necessary in sufficient amount to produce hormones like human growth hormone (HGH). If you aren’t absorbing or making enough of those amino acids, your production of that hormone will be lowered. People interested in fitness and bodybuilding goals, are interested in counteracting these down-regulations so that they can maximize bodies ability to perform and meet bodybuilding goals.