For some time, it has been realized that there must be local as well as systemic regulation of muscle growth. Using muscles thawere stretched and/or electrically stimulated my group cloned a RNA transcript that was only detectable in muscles that had been mechanically challenged. Because its expression was mechano sensitive we called it mechano growth factor (MGF). This is derived from the IGF-I gene but during the splicing process a reading frame shift is introduced which results in a different carboxy peptide so it differs from the systemic or liver type of IGF-IEa. MGF is produced as a pulse that peaks at about one day and work. Experiments with Professor Wernig of the University of Ulm indicated that this was the same time frame as the activation of the muscle satellite (stem) cells. Decreased expression of MGF has been found to be associated with muscle wasting. Studies in muscle in old rats and using elderly volunteers show an inability to produce MGF in response to resistance exercise. Experiments with Professor Kjaer's group in Copenhagen showed in older men improved strength was obtained with the administration of growth hormone and that this resulted in increased MGF levels. The evidence to date indicates that MGF is involved in reducing local damage, enhancing cellular repair and in inducing hypertrophy to adapt to increased overloa