T Nation


What can you guys tell me about IGF1 as what
is it ,and what relation does it have to HGH??

The insulin like growth factors (IGFI & II) were originally called the somatomedins because there were thought to mediate the effects of GH. In actuality, GH does stimulate IGF-I release, but IGF-I can also work in an autocrine or paracrine fashion on its own. That means that tissues such as muscle can produce IGF-I without the GH stimulation signal. When a muscle is exercised it may produce IGF-I and release it stimulating it’s own growth through receptor mediated activation. It will also stimulate growth of the cells around it. If you injure the muscle, IGF-I will be released from endothelial cells, inflammatory cells and the extracellular matrix, thus stimulating regeneration. This is one of the reasons eccentric exercise is such a strong stimulator of growth.

Exogenous administration of IGF is typically more effective than hGH, because you bypass the middle man so to speak. For hGH to have much of an effect it likely needs to stimulate IGF production. Resulting IGF levels will not be as great as with exogenous IGF administration and therefore hGH is less effect (at building muscle mass). There are probably some effects not necesarily related to muscle mass that hGH would benefit though.