Insulin-like growth factor 1 (IGF-1, somatomedin C) is an anabolic peptide hormone of 70 amino acids that is stimulated by growth hormone (GH) after birth and has pronounced growth-stimulating activity [1]. Given GH's low affinity for plasma proteins, it is rapidly eliminated from the blood, with a half-life of approximately 20 minutes. IGF-1 is synthesized 90% in the liver by GH stimulation, is released slowly and binds to six different IGF-binding proteins (IGFBPs), with IGF-binding protein 3 (IGFBP-3) responsible for 95 % of the bond in the circulation, and this extends the half-life of IGF-1 to approximately 20 hours. IGF-1 exerts insulin-like activity (anabolic, anti-catabolic, lipogenic, hypoglycemic), but in a weaker way, and can also bind to the insulin receptor, just as insulin can bind to the IGF- 1, but each hormone binds primarily to its own receptor.

Most studies indicate that IGF-1 acts in muscle regeneration through stimulation of satellite cells, and also in the formation of collagen, regeneration of articular cartilages (which is very good for athletes who are recovering from an injury) and genesis of new neurons [2]. “IGF - 1 is known as a cell differentiator. Differentiation is a process of signaling stem cells (stem cells, which have the best ability to divide giving rise to two cells similar to the progenitors) immature to become a specialized cell type, and in the case of IGF - 1 , the type of cell to be created is muscle. These newly formed muscle cells will remain muscle cells permanently and will retain the capacity for hypertrophy to the same degree as previously existing muscle cells. The process of transforming a stem cell into a muscle cell is known as hyperplasia. Hyperplasia other than muscle cell hypertrophy, in which hypertrophy is simply the growth of previously existing muscle cells, whereas hyperplasia leads to an effective increase in the number of muscle cells present. IGF-1 works side by side with MGF (mechanical growth factor), in order to carry out the hyperplasia process. FGM initiates this process through the proliferation of cells, which is the formation of new stem cells. Once these new stem cells have been manufactured, IGF - 1 can then perform its differentiation function, completing the hyperplasia process "[3].

Studies have shown that IGF-1 levels do not change with strength training, even if GH levels are elevated more than 10 times after training. However, an experiment showed that strength training increased “local” levels (in muscle, paracrine / autocrine isoform) of IGF-1 by about 500%. The autocrine / paracrine performance of IGF-1 has been demonstrated in studies involving the localized application of the peptide. In studies carried out in which GH and IGF-1 were used together, a greater increase in lean body mass and a reduction in fat was found than through the use of each compound alone [4]. Research also believes that the use of testosterone (androgens) also increases IGF levels in the muscle. Studies provide evidence that protein intake is a determinant of circulating IGF-1 levels in humans, and suggest that reduced protein intake may become an important component of anti-cancer and anti-aging dietary interventions [5]. This means that IGF works much better when you are eating enough protein (1.7-2 g / kg).

The most popular type of IGF-1 available on the black market is a more durable version (more amino acids), known as IGF-I Lr3. IGF-1 Lr3 (83 amino acids) is more potent (2-3x) than the smaller versions that are no longer available on the black market, as it has less affinity to be rendered inactive by IGF binding proteins. IGF-1 LR3 is most commonly injected once a day, every day or just on training days, before or after training. The effective dosage range is typically between 50-150 mcg per day (injected bilaterally into the muscles), although a small percentage of users exceed this dosage. It is not yet known the dosage limit at which LR3 ceases to have additional effects. Desensitization appears to occur after about 4 weeks of chronic use, at which point the individual has the option of discontinuing the peptide for a period of 2-4 weeks (after which he can re-use) or the individual may choose to increase the dosage in order to overcome desensitization and continue to experience its benefits. However, the desensitization process will continue to occur with each rising dose [3].

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