using clenbuterol to induce muscle hypertrophy also showed that BA treatment resulted in a significant upregulation of Cdkn1a mRNA abundance in skeletal muscle.CDKN1A inhibits cyclin-dependent kinase 2 activity, leading to irreversible cell cycle exit and terminal differentiation of myocytes (47).Satellite cells act as a source of new myonuclei during muscle repair and growth,whereas decreased p21Cip1 in aging skeletal muscle delays the withdrawal of satellite cells from the cell cycle and make them fail to differentiate, resulting in sarcopenia and impaired skeletal muscle regeneration (48). This evidence concerns the gene CDK2 and sarcopenia.