TTestosterone - The fact that the booster ( bodybuilding training ) the importance of testosterone levels has been known for a long time . It was found that in the practice of the bench there is leaching of testosterone , which is beneficial for the growth of muscle mass . Such a favorable level is only for a short training length of about 45 minutes of high intensity exercise . For prolonged low intensity ( especially endurance ) level drops sharply . If so built training often repeated , due to low levels of testosterone slows muscle growth , increase the time required for regeneration and leads to overtraining . This fact first put into practice Joe Weider , when wearing test the training , which is today known as double or . triple split system . One day not scheduled one practice unit , but two or three shorter of high intensity . Such training principle allow the testosterone levels remain at optimum levels long.