Although the mechanisms underlying age associated muscle loss are not entirely understood, researchers attempted to moderate the loss by increasing the regenerative capacity of muscle. This involved the injection of a recombinant adeno-associated virus directing overexpression of insulin-like growth factor I (IGF-I) in differentiated muscle fibers.

They demonstrated that the IGF-I expression promotes an average increase of 15% in muscle mass and a 14% increase in strength in young adult mice (Figure 1), and remarkably, prevents aging-related muscle changes in old adult mice, resulting in a 27% increase in strength as compared with uninjected old muscles (Figure 2). Muscle mass and fiber type distributions were maintained at levels similar to those in young adults. These results suggest that gene transfer of IGF-I into muscle could form the basis of a human gene therapy for preventing the loss of muscle function associated with aging and may be of benefit in diseases where the rate of damage to skeletal muscle is accelerated.