There are 70 inter-connected amino acids that make up a single chain of IGF-1. IGF-1 is a hormone that is produced when the liver is stimulated by human growth hormone. When levels of HGH rise in the blood, the liver responds by producing more IGF-1. These higher “bursts” spur growth and regeneration by the body`s cells, especially in muscle cells. Increases in IGF-1 levels have shown positive effects on increases in muscle strength, size, and efficiency. When you do not have enough IGF-1 in your body, whether caused by disease, malnutrition or a hormone imbalance, your growth can be stunted.