Free testosterone is that which has not been bound to other chemicals and is thus freely circulating and available to the receptors. The production of testosterone peaks in men around age 40. That must take a tremendous toll on the self image, self esteem, and feeling of power and aliveness in a man. The reduction in testosterone levels may even be one of the reasons that some men are not as productive after 55 or 60 years of age. A lot of these problems could be resolved by testosterone replacement therapy.
Testosterone accelerates growth in tissues that have testosterone receptors.
Receptors are cell components that combine with the hormone to alter the function of the cell. Since men have more testosterone, they have more muscle. Studies are currently being conducted to see if, and to what degree, testosterone affects both muscle mass and bone mass in men. Per George Debled, M.D., most of the tissues of the body have at least some androgen receptors Testosterone stimulates blood flow, precipitates aggressive behavior, determines fat distribution in men, causes deep voice, causes beard and pubic hair development, affects sex drive in both men and women, and affects sexual desire, thought, and fantasy. Testosterone affects many metabolic activities, as well as vigor and enjoyment of life.