Carbohydrates and the Athlete : The Key to Success
The more muscle mass a person has means the greater the potential for glycogen storage, which in turn means the greater need for glycogen. Greater glycogen storage means greater fluid storage, which is advantageous for the endurance athlete because they have excess body water to sustain their sweat rate.
Blood glucose is the primary source of fuel for the central nervous system. Derived from mainly dietary carbs mostly in the form of starches. Blood glucose is not easily maintained when liver glycogen is depleted.
Insulin and glucagon are pancreatic hormones that work together to control blood glucose. Insulin is secreted from the beta cells of the pancreas and is stimulated to secrete when there is high blood glucose (the higher the glucose, the higher the insulin response). The pancreas always is secreting small amounts in insulin in order to fuel tissue and brain cells. Insulin lowers blood glucose by affecting the cell membranes of muscle and fat cells, therefore allowing cells to receive a needed source for energy. In between meals and during exercise, low blood glucose may occur, therefore glucagon is secreted to break down liver glycogen and result in free glucose in the blood for fuel. Lower levels of glucose mean a greater production of glucagon.
Why are carbohydrates a critical fuel for athletes? What is its role in fat burning at different intensities of workouts?
Carbohydrates are critical fuel for athletes because carb stores and available free glucose are limited in supply therefore athletes have to make sure they maintain glycogen stores in order to sustain activity. Once the glucose from carbs are gone then the body goes for muscle glycogen stores, but low liver glycogen stores will then result in hypoglycemia, mental fatigue and then cause muscle fatigue. Factors like age, high altitude, long-duration activity and high-intensity activity increase the reliance on carbohydrates.
The total caloric requirement per unit of time is much greater in high-intensity activity than in low-intensity activity and the volume of fat burned is greater in high-intensity activity. Aerobic glycolysis can produce ATP for muscular work in larger quantity and at a faster rate than the oxidation of fat can produce it.
Why is fat not a primary source of energy for the athlete?
Fat can only be metabolized aerobically meaning that if you do any type of anaerobic activity then fat cannot be a source of energy. Since athletes store more fat calories than carbohydrate calories, it increases the ability to use fat therefore there is less of a reliance of carbs. Carbohydrate stores last longer. Medium-chain triglycerides are quickly oxidized for energy and rapidly catabolized into fatty acids and glycerol. Glycerol is burned like a carb and retains water.
The Role of Glycolysis for different types of athletic training
Glycolysis is a metabolic process that breaks down glycogen and glucose both aerobically and anaerobically through a series of reactions to either pyruvic acid or lactic acid and releases energy for the body in the form of ATP. This is the primary energy source for intense exercise for short periods.
In high-intensity training, the higher the activity means the faster the ATP must be regenerated. In activities where intensity exceeds the capacity to bring sufficient oxygen into the system to meet the energy demands, anaerobic glycolysis becomes the major pathway for ATP production. Extreme high-intensity exercises can only last between 1.5 to 2 minutes because anaerobic exercises are self-limiting due to the lactic acid buildup.
In steady, low-impact exercises, ATP can be adequately produced aerobically from the oxidation of carbohydrates and fat. The oxygen system is used in the aerobic production of ATP and can be used for long periods of time without the production of system-limiting by-products.
Aerobic glycolysis is used for high-intensity exercise that requires a large volume of ATP but is within the athlete’s capacity to bring in sufficient oxygen into the system. Aerobic production of ATP from the breakdown of glycogen is expressed.
The phosphocreatine system is characterized by the anaerobic production of ATP from stored phosphocreatine and used for maximum-capacity activities.
Why is rapid recovery important for an athlete?
Rapid recovery is important for an athlete because during training, they need adequate nutrition in order to replace glycogen stores in the muscles and allow for muscle and tissue repair. The key to optimum recovery is nutrition. Timing is important because of the rate of digestion and amount of blood sugar can affect the performance of a race. High training loads require a greater intake of carbohydrates for short-term replenishment of glycogen stores that have been used, therefore a low to moderate glycemic index foods should be eaten in order to optimize athletic performance.
When are carbohydrates needed and utilized to enhance training outcomes? Why?
Immediately after and up to 4 hours after exercise, athletes should consume at frequent intervals, 1.0 to 1.2 grams of carbohydrates per kilogram of body mass per hour.
For daily recovery from moderate-duration low-intensity training, athletes should consume 5 to 7 grams of carbs per kg of body mass per day.
Daily recovery from moderate to heavy endurance training suggests 7-12 g of carbs per kg of body weight per day.
Daily recovery from extreme exercise that includes 4+ hours per day suggests 10-12 g of carbs per kg of body weight per day.
Physical activity increases the rate of energy expenditure and athletes need to strategize amount of intake based out their desired outcomes. Sufficient energy intake is needed to support total energy requirements including tissue repair, tissue maintenance, and growth and energy requirements itself. Athletes must consume enough carbs in order to optimize glycogen stores, allow for muscle recovery after exercise, sustain blood sugar and provide a well-tolerated source of energy.
The Week Prior to a Race
The week prior to a race, depending on what type of priority the race is, they should decrease training and decrease the amount of food. The day before a race, an athlete should eat more carbohydrates, but make sure to include protein and fat in those meals. During this time, an athlete should eat more fruits like bananas, melons, peaches and vegetables such as potatoes, sweet potatoes and yams. Protein and fat should be eaten with every meal such as fatty fish and flaxseed oil. It is also important to reduce fiber to allow for easier digestion and add salt to the diet if the event will be in a hot climate or for extended amount of time.
The Day of the Race
Preexercise eating goals should focus on eating at least 2 hours before they exercise, restocking their carb stores that were depleted from the night before as well as fluid. They should consume 200 to 300 calories per hour prior to exercise and take in mostly carbs. Their meal should have a reduced glycemic index in order to slowly replenish glycogen stores, for example fructose from fruit would be a good choice but make sure there is low fiber. Also make sure to include protein especially BCAA in the meal because essential amino acids in addition to carbs will allow for faster recovery because it stimulates protein synthesis after exercise. BCAA’s also improve the time to exhaustion and allows for maximum power output. In addition to low GI carbs, protein allows for a slower release of sugar therefore decreases fatigue. Water should be taken in the last hour. Foods that are good before exercise include fruit and an egg, applesauce with protein powder, baby food, liquid meals and protein bars. 10 minutes before start, the athlete should consume 100 to 200 calories followed by 6 to 8 ounces of liquid.