Abstract: The skeletal muscle presents a great adaptation capacity to the external factors, the importance of contractile activity in determining the muscle phenotype is widely recognized. The studies initiated in the ’80 of the previous century reprezented the debute in the research of the structural and functional modifycations produce at the specific gene expression. The knowledgement of these aspects offers the posibility of obtaining great athletic performances and it denies the absolut importance of the genetic predisposition, as it was known.

Key words: specific gene expression, contractile activity, detraining.