INSULIN AND MUSCLE
Insulin is actually a protein, and it is produced and released by the pancreas whenever you eat carbs, protein, or both. (That is, if the pancreas is working properly). Yet unlike the proteins that are the physical building blocks of muscle, this is a functional protein, much like growth hormone.
Like all other proteins, insulin is a chain of amino acids strung together. But the way this protein chain is folded makes it act more like a signaling mechanism than a building block.
From the pancreas, insulin enters the blood stream and travels to various tissues, including muscle tissue. The muscle fibers (or cells) are lined with insulin receptors, similar to a docking station. Once the insulin molecule docks onto the receptor, it signals the muscle cell to open up gates. This allows allow glucose, amino acids, and creatine to enter the muscles. This process is a major reason why insulin is so important for building muscle.
Another reason is that when insulin docks onto the muscle cells, it instigates biochemical reactions in the muscle that increase protein synthesis, which is the building of muscle out of the amino acids that are entering the muscle cells. In addition, insulin also decreases muscle breakdown, which further enhances muscle growth.
Insulin also indirectly aids in muscle development by causing the blood vessels to relax and dilate, allowing greater blood flow to the muscles. By increasing blood flow, insulin can help get even more nutrients like glucose and amino acids to the muscles. This is why you'll see bodybuilders pounding simple carbs on contest day. Not only does the corresponding spike in insulin drive the carbs into the muscles to keep them full, it also boosts vascularity.
http://www.bodybuilding.com/fun/the-...o-insulin.html