Testosterone, also known as androgen, is a naturally occurring hormone produced in the testes in men, and small amounts are produced by the ovaries and adrenal cortex in women. Testosterone is a vital hormone responsible for the development of secondary sexual traits, as well as increasing muscle size and strength. Testosterone is best and it will always be the best muscle-builder - the more you have, the better, and of course…the faster you’ll build muscle and get freaky huge!