Carbohydrates:
The Fuel Of Choice!!!!!
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Carbohydrates:
The Fuel Of Choice!!!!!
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The most important components of an athlete's diet are carbohydrates (CHO), fluids, and energy.The secondary components of the diet are protein, vitamins/minerals, fats, maintaining body weight, and supplement use.
As you can see, CHO are a part of the most important components of an athlete's diet.
Carbohydrates have many important functions in the body:
1. Replenish glycogen stores
2. They are the preferred fuel for the brain/body
3. CHO-loading may improve performance with some activities
***If you exercise for more than 1 hour, you will need more CHO for fuel.***
The athlete's diet should consist of at least 55% and up to 75% of the total calories per day. You can obtain CHO from various breads, cereals, pasta, fruits, vegetables, and some dairy products.
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An Athlete's Diet |
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Studies show that a diet containing only 45-50% of CHO is not high enough for the athlete. A high CHO diet is required for adequate glucose storage and utilization. A rest day is also important for repletion of the muscle glycogen stores. We can look at the glycemic index of foods to see how much glucose we will be absorbing. Foods that have a high glycemic index are sports drinks and simple sugars. These foods are absorbed very quickly into the bloodstream and raise blood sugar values rapidly. Rice is a food that has a medium glcemic index. Foods such as peas, corn, and other foods high in fiber have a low glycemic index. It takes the body longer to digest these foods so the rate of absorption is that much slower. The limitations of what can influence the glycemic index of foods are the form of the food, cooking time/style, food combinations, food processing, amounts and types of fiber present in the diet, and individual differences. Everybody's insulin response is going to be different, especially if they are a diabetic. During exercise, the insulin secretions are relatively low so the body must tap into its stores for energy. You do not want to have food in your stomach before an event. It is probably best to eat your meal at least 3-4 hours before your event. You want your stomach to be empty at the time of the competition. Food in the stomach may lead to cramps, which could hinder performance. You also do not want to eat a meal that is high in fat or protein. A high CHO meal is best because it is digested that much faster than the fats and protein and your body wants that extra energy in the form of CHO, rather than fats or protein. It is also a good idea to consume fluids along with the meal and right up to the event. We will talk about fluid requirements later.
There are a few fates for the CHO that is ingested. It can be absorbed
immediately into the bloodstream and be used for energy, can be stored as
glycogen, or can be converted or stored in the form of fat. The approximate
CHO stores in the body are:
1. Blood glucose --5 grams
2. Liver glycogen --75-100 grams
3. Muscle glycogen --300-600 grams
***The energy value for CHO is 4 kcals/gram. An individual has approximately 20 kcals in the blood, 300-400 kcals stored in the liver, and 1,200-2,400 kcals stored in the muscle. We can see why we want to eat a high CHO diet. We need to replace all that is lost during exercise. The longer the exercise, the more CHO depletion. The depletion of CHO stores can lead to mental and physical fatigue, which can both hinder performance.***
Carbohydrate Loading |
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Muscle glycogen depletion is a limiting factor in endurance exercises that
exceed 90 minutes in duration. It has been proven that some athletes
may come close to doubling their muscle glycogen stores. An athlete
may not exceed the 600 grams that can be stored in the muscles. The
body can not store any more than that.
There was an older model for CHO loading, but there were many drawbacks to that particular method. Recently, a new technique was published that reduces the problems with the other method. Six days before the competition, the athlete needs to exercise hard at 70-75% of their aerobic capacity for 90 minutes in duration. On this day and the next two, the athlete consumes a diet of approximately 50% CHO. On the second and third days, the athlete only exercises at 70-75% of their aerobic capacity for 40 minutes in duration. The next two days the athlete should consume approximately 70% of their calories from CHO. They should reduce their training on these days to 20 minutes at 70-75% of their aerobic capacity. The last day the athlete should rest and continue with the high CHO diet. This type of loading is not going to enhance performance within the first hour of the activity, but it will after 1 hour of duration. It has been shown that runners can run faster after 1 hour with a CHO loading regimen. The CHO loading increases the muscle glycogen stores and allows the athlete to perform at a competitive level for a longer period of time.
Some considerations to take into account before attempting to CHO load are:
1. Make sure you are aerobically trained --endurance training stimulates the enzyme glycogen synthase, which is responsible for glycogen storage
2. As more CHO is stored, the more water is stored --this may lead to a feeling of stiffness and heaviness, but symptoms will disappear with exercise.
3. CHO loading will only help athletes who are going to be competing in endurance events lasting longer than 90 minutes.
4. Tapering of the activity is essential and the training exercise should be the same as the competing event
5. Diabetics should consult a physician before starting
Carbohydrate Intake Before Exercise
The Pre-Exercise Meal:
1. It will not contribute immediate energy, but may be helpful with events lasting longer than 90 minutes.
2. Helps to replenish CHO stores, just in case they were low.
3. Will help to delay fatigue with prolonged exercise.
Recommended Intake:
CHO Intake During Exercise
The Exercise Meal or Drink:
1. Once again, important for events lasting longer than 90 minutes.
2. May help to increase endurance times by 30-60 minutes.
3. Provides glucose to the muscles and maintains blood glucose levels.
Recommended Intake
The Post-Exercise Meal
Eating After the Event:
1. The rate of muscle glycogen repletion is fastest within the first two hours after the exercise. Very important to eat after the event to adequately replace CHO stores.
Recommended Intake
Carbohydrate Metabolism
Glycolysis:
1. Anaerobic (without oxygen):
Glucose ----------> 2 ATP + Lactic
Acid
2. Aerobic Glycolysis (with oxygen):
Glucose + oxygen ----------> 36 ATP +
CO2 + H2O
1. Intensity
Reasons for this:
2. Duration
***Intensity of the exercise drives which fuel source
will be used and duration modifies it.***
Link to Adaptations of
Training
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