To strengthen the anabolic properties of testosterone, more than 100 synthetic steroid derivatives have been described for human purposes. The anabolic effect promotes protein synthesis, muscle growth and erythropoiesis. In clinical practice, substances with anabolic effect are needed to overcome various catabolic states. However, none of these compounds are devoid of androgenicity. Androgenic and anabolic properties of anabolic steroids cannot be totally separated. Therefore, it is more appropriate to use the term anabolic androgenic steroids (AAS).
So, for instance, increases in plasma testosterone commonly observed following a hard weight-training session are not just the result of increased production of testosterone from the testes, but also from a reduction in its clearance blood flow to the liver and kidneys is reduced during exercise. This balance between synthesis and breakdown also make a single blood testosterone value extremely difficult to interpret. As noted decades ago, testosterone levels rise and fall throughout the day; therefore a single testosterone value could represent a peak or valley on the daily testosterone roller coaster.