Growth Hormone (GH or HGH) is a key hormone that helps us build muscle and burn fat.

Your muscles are made of cells that have been fused together into muscle fibers. And on the outside of these fibers are things called satellite cells.

When you work out you damage cells in the muscle fibers. To fix this, your body releases Growth Hormone, Growth Factors (other hormones) and Testosterone. These tell the satellite cells to start replicating to both repair and replace damaged cells in the muscle, and also to add more cells, increasing the muscle fibers in size.