Adaptation of human skeletal muscle to training and anabolic steroids

Understanding the cellular and molecular adaptations of skeletal muscle in response to strength training is important to provide frameworks to improve performance of elite and recreational athletes as well as the health and q uality of life of the general population with or without chronic diseases. This work was mainly devoted to some of the aspects related to the enlargem ent of human skeletal muscle in response to short and long-term strength tr aining and the administration of anabolic steroids. There are a number of f undamental questions related to the cellular mechanisms underlying the hype rtrophy of muscles that have received little attention. Likewise, the mecha nisms behind the myotrophic action of anabolic steroids on human skeletal m uscles are still not well understood. The question whether adaptational cap acity differs between neck/shoulder and limb muscles was also addressed. Mu scle biopsies were taken from the trapezius and the vastus lateralis muscle s. Muscle fibre types, fibre area, myonuclear and satellite cell number, an d androgen receptors (AR) expression were evaluated using enzyme-immunohist ochemistry. Myosin heavy chain (MyHC) content was determined using biochemi stry. It has been demonstrated that muscle fibres containing MyHC IIA are increas ed following strength training. It was shown for the first time that the ac quisition of additional myonuclei is required to support the hypertrophy of human muscle fibres in response to strength training. Additional myonuclei incorporated into hypertrophying muscle fibres are derived from satellite cells. In this respect, it was shown for the first time that strength train ing induced a significant increase in satellite cell content in skeletal mu scle. This indicates that training induced the activation of muscle stem ce lls that started to generate, by a series of asymmetric cell divisions, dau ghter cells that became satellite cells. It was also shown that new muscle fibres are formed following strength training. When training produces the f ormation of new muscle fibres and does not induce the degeneration of pre-e xisting fibres, muscle hyperplasia occurs in human skeletal muscle. With re gard to the use of anabolic steroids, it was demonstrated that their usage further enhance the effects of strength training (fibre hypertrophy, myonuc lear increase and new fibre formation), All these changes occur both in the trapezius and the vastus lateralis. Regarding AR in human skeletal muscle, it was found that they are expressed in myonuclei and in capillaries. The number of AR-containing myonuclei was higher in the trapezius than in the v astus lateralis. Strength training is associated with an increase in AR-con taining myonuclei only in the trapezius. The use of anabolic steroids furth er increases AR-containing myonuclei in the trapezius. Thus, the regulation of AR content following training is muscle dependant.