Skeletal muscles are able to adapt to over - or under-use. In response to enhanced use, such as exercise, skeletal muscles undergo morphological and physiological changes possibly including injury and regeneration of muscle fibers (myofibers). The regeneration process includes addition or replacement of myofiber nuclei (myonuclei) (1). Myonuclei are terminally differentiated, thus maintenance and repair of myofibers are attributed to satellite cells, the myogenic stem cells. Up to date little is known about the differential effects of different growth factors on satellite cell and their subsequent contribution in exercise. The adaptation of skeletal muscles to altered use is governed by three major processes: satellite (stem) cell activity, gene transcription, and protein translation. A defect in any of these processes could interfere with muscle maintenance and regeneration. This review focuses on current understanding of the effects of resistance and endurance exercise on skeletal muscle fibers (myofibers) and on the skeletal muscle stem cells, satellite cells. We first summarize in brief the basic biology of skeletal satellite cells; the types of exercise and the basic biology of IGF-I. We then discuss the interplay between IGF skeletal muscle and satellite cells.