Research on mechano growth factor: its potential for optimising physical training as well as misuse in doping.

T he sequencing of the human genome showed that there are only about 40 000 genes. However, there are many more proteins. This is because some genes are spliced to produce different protein/peptides which usually have different biological functions. Combining physiological and molecular biology methods made it possible for our team to identify and characterise a local muscle growth/repair factor (MGF). This we found is derived from the insulin-like growth factor I (IGF-I) gene by alternative splicing, but, owing to a reading frame shift, MGF has a unique C-terminal peptide. After resistance exercise, the IGF-I gene is spliced towards MGF which ‘‘kick starts’’ hypertrophy and repair of local muscle damage by activating the muscle stem cells as well as anabolic processes. Interestingly, loss of muscle mass in old age and in certain diseases is associated with an impaired ability to express MGF. In these conditions it seems that the muscle stem (satellite) cell pool is not adequately replenished.