What is insulin and how does it work?
Carbohydrates, specifically glucose, is the primary energy source during vigorous exercise. Carbs are the human body's key source of energy and glucose is the principal fuel for the brain. Any extreme fluctuations in blood glucose levels can be extremely dangerous; too little can inhibit performance, whereas too much can damage the vascular system. Control of blood glucose is regulated by the pancreas, which produces two specific hormones: insulin and glucagon.
Insulin helps regulate energy and glucose metabolism in the body. After consuming a meal, glucose enters the blood at the small intestine, causing a rise in blood glucose levels. As the blood is circulated through the pancreas, elevated levels of glucose trigger the release of insulin. The insulin then binds with the receptors of its target cells. Glucose then diffuses out of the bloodstream and into the cell. The net result is a drop in blood glucose levels. This, insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle. (In other words, the energy you would then use to exercise)
How does exercise effect all of this?
As activity levels increase, glucose uptake by the cells also increases. This is the result of an increased sensitivity of the cells to insulin; thus, insulin levels will drop during physical activity. At the same time, glucagon secretion by the pancreas increases, this helping maintain a steady supply of glucose.
So this is an in depth summary of what happens with your body when you intake carbs. Long story short, your body needs carbs for energy to withstand those vigorous workouts that we recommend that will produce the results you're looking for!