For those who exercise intensely for 1½ or more hours/day, refueling during exercise is sometimes beneficial. Marathon runners, elite athletes, and recreational sports participants who practice and train on a regular basis should pay extra attention to replenishing fluid and nutrient losses to maintain their blood sugar levels and maximize performance.
Initial energy comes from glycogen stores that are readily available in the muscles. As these stores are depleted, energy from blood sugar is used for fuel, which may cause feelings of fatigue. Blood sugar is necessary for thought, concentration, and focus; so, it is essential to maintain levels during exercise.
The American College of Sports Medicine recommends 30-60 grams (g) or 100-250 calories of carbohydrates/hour during endurance exercise, after the first hour. This translates to 16 fluid ounces (fl oz) of a sports drink or juice (49 grams of carbohydrate), an energy bar (carbohydrate content varies among bars; look for one that contains around 30 grams carbohydrate), or a medium-sized banana (around 30 grams of carbohydrate).
As blood glycogen is depleted, the body relies on blood glucose for energy. Carbohydrates provide added fuel, and prevent the fatigue and crashes that are associated with low blood sugar.
Both fluids and foods provide the same energy to the body, if they are carbohydrate-rich sources. Athletes should try a combination of food and drinks to determine what is best tolerated. Many athletes choose:
- Fruit
- Juices
- Sports drinks
- Hard candy
- Energy bars and gels
Keeping snacks accessible is important. Marathon runners, cyclists, and distance athletes may choose to have foods placed at various spots and mile markers on the course to prevent crashes. Endurance athletes should weigh themselves before and after a long bout of exercise to determine hydration requirements. Loss of 1 pound through sweat and fluid losses requires 13-16 fl oz repletion, preferably with water.
If exercise is longer than 4 hours in duration, the athlete should prepare for the event by consuming a slightly higher than usual amount of sodium the week before. This will help to prevent hyponatremia, which may cause fatigue, nausea, headaches, and seizure.
Cramping may result from dehydration, lack of calcium, lack of potassium, or insufficient sodium. Recommendations for preventing nutrition-related cramping include extra intake of fluids, low-fat dairy products, and fruits and vegetables rich in potassium, or consumption of foods that contain sodium.
The serious athlete should meet with a registered dietitian who specializes in sports nutrition. These nutritionists, who are trained to work with the demands of competition and the needs of the elite athlete, are the best source for nutrition information. They can tailor a training meal plan to promote best performance and meet the needs of the individual athlete.
