Loss of muscle mass and strength is a major problem during aging and the expression of Mechano Growth Factor (MGF), a member of the IGF-1 (insulin-like Growth Factor 1) super family, has been shown to be both exercise and age dependent. MGF, also called IGF-1Ec, has a unique E domain with a 49 bp insert in humans (52 bp in rodents; IGF-1Eb), which results in a reading frame shift during the IGF-1 gene splicing to produce a distinct mature isoform. We have studied the effects of the MGF-24aa-E peptide on proliferation and differentiation of primary human muscle cell cultures isolated from healthy subjects of different ages. We found that MGF-E peptide significantly increases the proliferative life span and delays senescence of satellite cells isolated from neonatal and young adult but not from old adult muscle, hypertrophy associated with a significant decrease in the percentage of reserve cells was observed in all cultures. It is concluded that the MGF-24aa-E peptide alone has a marked ability to enhance satellite cell activation, proliferation and fusion for muscle repair and maintenance and could provide a new strategy to combat age related sarcopenia without the oncogenic side effects observed for IGF1.