US EPA

7353412 

Journal Article 

Adaptation of human skeletal muscle to training and anabolic steroids 

Kadi, F 

2000 

Yes 

Acta Physiologica Scandinavica
ISSN: 0001-6772
EISSN: 1365-201X 

168 

2-52 

WOS:000086016600001 

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 quality of life of the general population with or without chronic diseases. This work was mainly devoted to some of the aspects related to the enlargement of human skeletal muscle in response to short and long-term strength training and the administration of anabolic steroids. There are a number of fundamental questions related to the cellular mechanisms underlying the hypertrophy of muscles that have received little attention. Likewise, the mechanisms behind the myotrophic action of anabolic steroids on human skeletal muscles are still not well understood. The question whether adaptational capacity differs between neck/shoulder and limb muscles was also addressed. Muscle biopsies were taken from the trapezius and the vastus lateralis muscles. Muscle fibre types, fibre area, myonuclear and satellite cell number, and androgen receptors (AR) expression were evaluated using enzyme-immunohistochemistry. Myosin heavy chain (MyHC) content was determined using biochemistry. It has been demonstrated that muscle fibres containing MyHC IIA are increased following strength training. It was shown for the first time that the acquisition 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 training induced a significant increase in satellite cell content in skeletal muscle. This indicates that training induced the activation of muscle stem cells that started to generate, by a series of asymmetric cell divisions, daughter cells that became satellite cells. It was also shown that new muscle fibres are formed following strength training. When training produces the formation of new muscle fibres and does not induce the degeneration of pre-existing fibres, muscle hyperplasia occurs in human skeletal muscle. With regard to the use of anabolic steroids, it was demonstrated that their usage further enhance the effects of strength training (fibre hypertrophy, myonuclear 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 vastus lateralis. Strength training is associated with an increase in AR-containing myonuclei only in the trapezius. The use of anabolic steroids further increases AR-containing myonuclei in the trapezius. Thus, the regulation of AR content following training is muscle dependant. 

human; hyperplasia; hypertrophy; myonuclei; myosin heavy chain; satellite cells; skeletal