Carbohydrate Consumption and Endurance Performance
Depletion of the body’s carbohydrate stores has been shown to be a primary limiting factor in endurance exercise performance. Because the body has a limited capacity for storing carbohydrate, proper dietary consumption is important in optimizing endurance exercise performance.
Endurance athletes and athletes who perform a high volume of short, repeated, high-intensity efforts can maintain their carbohydrate levels by consuming 5-10 grams of carbohydrate per kilogram of body mass each day. While a great deal of these carbohydrates can be consumed as part of a normal diet, event specific carbohydrate consumption requires specific techniques.
The pre-event meal includes those foods that are consumed within a few hours of the start of competition or a training session and should be primarily restricted to carbohydrates. For a long event such as a marathon, the athlete should consume approximately 5 grams of carbohydrate per kilogram of body mass approximately 3-4 hours before competition begins. Smaller amounts of liquid and semi-solids can be consumed up until approximately 1.5 – 2 hours before the start of the race.
Carbohydrate consumption during events lasting longer than 2 hours should be limited primarily to liquid and semi-solid sources for running with the addition of solid foods for activities such as bicycling. Consumption levels should be approximately 40-60 grams of carbohydrate per hour.
Post-exercise carbohydrate consumption is very important in maintaining carbohydrate levels. The muscle cell is much more permeable to carbohydrate in the minutes following exercise than it is several hours after exercise has ceased. Providing large amounts of carbohydrate immediately after exercise increases the rate of carbohydrate storage and helps the athlete to recover more quickly than if equal amounts of carbohydrate are consumed several hours after the end of exercise. Strive to consume 1.25 grams per kilogram immediately after exercise and then continue to consume approximately 1 gram per kilogram every two hours for 6 hours.
The type of carbohydrate consumed is important. Glucose is the only carbohydrate that the body can use in our energy pathways. All other dietary forms of carbohydrate must be converted into glucose before we can use it. Glucose is also quickly absorbed and promotes the absorption of water from the intestine. These traits make glucose a quick source of energy and useful in staving-off dehydration. Fructose, which is the sugar that is found in fruits, is not as easily absorbed from the intestine and must be converted into glucose before it can be used for energy. These two traits can slow the delivery of carbohydrate to the muscle and can result in stomach aches if fructose accumulates in the intestine. However, adding small amounts of fructose to energy drinks and gels improves their taste and improves their effectiveness by encouraging increased consumption.
Finally, don’t become a carbohydrate junky. These recommendations are for athletic populations who are undergoing serious training. If you are simply doing 30 minutes of exercise, three times a week, you run virtually no risk of becoming glycogen depleted. Undertaking the above recommendation under these types of circumstances could result in unwanted weight gain.