Testosterone is the hormone that boosts all bodybuilders towards greatness. It is the thought of as the key hormone that separates men from woman (woman make testosterone at 1/10 the amount). Testosterone gives males their characteristics such as confidence, aggressiveness, sex drive, increased muscle mass, facial hair, and a deep voice.
Higher than average levels of testosterone can significantly help men gain muscle and lose fat much easier than woman. Testosterone is one of the most important hormones in the body for anyone trying to gain muscle and lose fat.