Preferably, the muscle specific GHRF expression system is constructed in a plasmid vector. The complementary DNA (cDNA) sequences encoding GHRF signal peptide and GHRF itself were designed from the published peptide primary structure and optimized for mammalian codon usage. This cDNA is synthesized using conventional oligonucleotide synthesis chemistry. The GHRF and its signal peptide encoded by the cDNA sequences can be the corresponding natural or recombinant or synthetic, or biologically active fragments or their analogues with similar activities. The GHRF leader sequence encodes a signal peptide in the nascent GHRF peptides that will direct the export of said GHRF peptides out of the muscle cells and secretion into the general circulation in an active form.