steroids have been a subject of great interest in recent years. However, animal studies have given contradictory results, ranging from an insignificant effect [1] to improvement in physical working capacity [2], strength [3] [4] [5] , protein synthesis [6], lysosomal and mitochondrial activities [7] , and functioning of the sarcotubular system [8] . In general, many factors make it difficult to compare results, such as the species used, the gender and age of animals, the type of muscle studied

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... 3, [9] [10] [11] , experimental conditions, the specific anabolic androgenic steroids used [12], the doses, the mode and period of administration [6, [13] [14] [15] , and the diet [5]. In skeletal muscle, contraction is generated when action potentials invade the interior of individual fibers along the membrane of the transverse tubule system (T-tubule). The passage of the action potential is followed by an increase in free myoplasmic calcium concentration that activates troponin and allows crossbridge cycling and contraction. Changes in Ca 2ϩ concentration depend on an interaction between different processes: T-tubule action potential, voltage-sensor response, putative excitation-contraction coupling mechanism, the properties of the Ca 2ϩ release channel, Ca 2ϩ diffusion to and through myofibrils, Ca 2ϩ binding to myoplasmic calcium buffers, and calcium removal by sarcoplasmic reticulum Ca 2ϩ ATPase