Muscle stem cells (or muscle satellite cells [MuSCs]) are required for postnatal growth. Yet, the detailed characterization of myogenic progression and establishment of quiescence during this process remains poorly documented. Here, we provide an overview of myogenic cells heterogeneity and dynamic from birth to adulthood using flow cytometry. We demonstrated that PAX7+ cells acquire an increasing ability to progress in the myogenic program from birth to adulthood. We then simultaneously analyzed the cycling state (KI67 expression) of the MuSCs and progenitors (PAX7+) and their progression into myogenic precursors (PAX7−MYOD+) and differentiating cells (MYOG+) in vivo. We identified two distinct peaks of myogenic differentiation between P7–P10 and P21–P28, and showed that the quiescent MuSC pool is established between 7 and 8 weeks of age. Overall our study provides a comprehensive in vivo characterization of myogenic heterogeneity and demonstrates the highly dynamic nature of skeletal muscle postnatal growth process.