A general misconception is that insulin is only involved in energy and fat metabolism. When energy needs are high, insulin transports sugar from the blood into the muscle where it can be converted into energy. When energy needs are low, insulin facilitates the conversion of excess sugar into fat where it can be stored for future use.
What is often overlooked is the powerful effect of insulin on stimulating muscle protein growth and repair. An essential action of insulin is to increase the transport into muscle of amino acids, the building blocks of protein, where they can be used for rebuilding and repair. Insulin’s anabolic effects do not end there. Insulin also plays an important role in turning on one of the metabolic switches that control protein synthesis.
This action explains why combinations of carbohydrate and protein are far more effective in stimulating protein synthesis than protein alone. Two switches are responsible for turning on protein synthesis. One is activated by protein, specifically amino acid levels in the blood, and the second by insulin. Consuming carbohydrate (which raises insulin levels) and protein in your recovery drink gives you a dual benefit. In fact, research has shown that a carbohydrate protein drink is 38% more effective than a protein drink in stimulating muscle protein synthesis post exercise.
Another important effect of insulin is inhibition of protein breakdown. At any given time, muscle protein is in a state of flux – it is being synthesized and broken down. When more protein is synthesized than broken down, you have a net gain in lean body mass. After exercise, protein degradation is higher, primarily because during extended endurance activity up to 20% of the working muscle’s energy is derived from protein. That’s why consuming protein in your sports drink offers significant advantages. It reduces the amount of muscle protein used for energy. Higher breakdown rates of protein after exercise increases muscle soreness and slows the overall recovery process. By inhibiting protein breakdown, insulin mediates a faster recovery.
The bottom line – by taking advantage of how and when insulin works and how nutrition can affect insulin activity, endurance athletes can optimize muscle recovery and achieve significant improvements in endurance performance.