While athletes and some researchers believe that testosterone produces a mass improvement in performance and endurance, others believe that it cannot produce overnight effects. It cannot give a jolt of energy to sportspersons in order to improve their performance, since testosterone acts over time to build muscle and strength in the athlete. But even then, there has to be a considerable amount of effort (in terms of exercise) on the part of the athlete. Simply taking testosterone without any exercise or a suitable diet will only do more harm than good.
NOTE: One interesting fact about erythropoitin is that it is also called EPO, a name that may be more familiar to some of you. Yes, that should bring the name Lance Armstrong to mind. Lance Armstrong confessed to using EPO as a performance enhancing drug strictly for the purpose of raising his red blood cell counts for racing purposes. Basically, he was doing a different and very dangerous kind of steroid. Giving EPO to these racers leaves them vulnerable to dieing in their sleep from the "sludging" of the blood that occurs. It does turn them into superhumans however.