Carbohydrate supplies approximately 45-55% of the body's total energy (calorie) needs. Carbohydrate is also an essential fuel for prolonged sports. Exercise at high altitudes and in very cold temperatures also increase carbohydrate use. During very light exercise, fat is an important energy source. As exercise becomes more intense, carbohydrate becomes the preferred energy source as muscle glycogen (sugar) and plasma oxidation rates increase with every increment in exercise intensity. As the muscle glycogen is being used during exercise, blood glucose enters the muscle tissues. In turn, the Liver will release some of its glucose to help maintain or elevate blood glucose to prevent hypoglycemia.
As you initiate an exercise program, a major portion of your energy will be derived from your muscle glycogen stores. Lactic acid, a byproduct of glycogen metabolism produced in the muscle during intense exercise, may be released into the blood and carried to the liver for reconversion to glucose. The glucose may then return to the muscles to be used as an energy source or stored as glycogen. This is referred to as the Cori Cycle, or the working metabolism with-in the muscle cells. Lactic acid results from limited oxygen to the muscle cells during exertion; accumulation results in muscle fatigue, cramping or pain. To help relieve the pain, relax the muscles frequently to help the circulating blood carry the the lactic acid back to the liver for "recycling." Proper breathing during exercise is important to help prevent lactic acid formation. Beverages containing caffeine have shown to help relieve muscle soreness after exercise, and some athletes claim that Coenzyme Q10 has helped prevent lactic acid buildup, as it helps supply needed oxygen to the muscle cells.
A diet rich in complex carbohydrates not only have several major health benefits, but also help guarantee optimal energy sources for daily exercise training. There is no evidence that diets which restrict carbohydrate ( such as the Zone Diet) enhance training.