Insulin Growth Factor or IGF-1 is a protein that has clear cause-effect relationship with muscle hypertrophy. IGF-1 is stimulated by growth hormone (GH) and its anabolic effect increases with mechanical loading resulting in increase in strength. Although GH is associated with collagen synthesis, IGF-1 is not. It is only associated with muscle hypertrophy. IGF-1, apparently, has 1 main function and it is to fuse satellite cells or stem cells into existing muscle fibers. During mechanical strain produced with resistance training creates minimal muscle damage which creates leakage of GH to initiate repairing of the fibers and it activates the IGF-1. The IGF-1 then fuses the satellite cells which start acting as myocytes which repair the muscle fibers and grow them. This is essential since the nuclear-content-to fiber mass ratio is limited, and these new myocytes become important in creating muscle mass. With the help of BFR and the metabolite theory, hypertrophy training has shown more IGF-1 than in high resistance protocol since increased lactate from the use of the BFR creates more GH; which in turn activates more IGF-1.
Abe et al found a significant increase in IGF-1 compared to the control work group. Along this, they found increased Cross Sectional Area of the muscle fiber and strength. The key is to increase the metabolites to activate these pathways. Multiple studies have shown increases in these satellite cells, along increments in strength and hypertrophy in groups that undergo BFR training vs traditional high resistance training or control groups.
This information was obtained from Owens Rehab Sciences.