If you eat a normal runner ’s diet, with about 60 percent of your calories from carbohydrate, you probably store about 1,500 to 2,000 calories of glycogen in your muscles. If you glycogen load, however, your muscles have the capacity to store between 2,000 and 2,500 calories of glycogen. Each mile (1.6 km) that you run burns about 90 to 140 calories, depending on your weight and metabolism, and 75 to 90 percent of those calories are supplied by carbohydrate. If you do a great job of loading, you’ll have just about enough glycogen for the marathon.
Glycogen loading is also important before your long runs. Make sure to eat a high-carbohydrate diet the day before your long run so that you have plenty of fuel to go the distance. Carbohydrate loading before your long runs will help ensure that you have high-quality long runs, which will increase your confidence for the marathon.
Your daily carbohydrate requirement depends on your weight and how much you’re training. If you’re averaging an hour to an hour and a half of training per day, you need approximately 7 to 8 grams of carbohydrate per kilogram (3 to 3.5 g/lb) of your body weight per day. If you’re training for 2 hours or more per day, you need approximately 9 to 10 grams of carbohydrate per kilogram (4 to 4.5 g/lb) of body weight per day.
As an example, say Gary is running 80 miles (129 km) per week and weighs 154 pounds (70 kg). His average daily training time is about 80 minutes. Gary’s daily carbohydrate requirement is 490 to 560 grams (70 × 7 to 70 × 8). Each gram of carbohydrate supplies 4.1 calories, so Gary’s calorie supply from carbohydrate should be 2,000 to 2,300 per day.
With a typical runner’s high-carbohydrate diet, you probably have enough glycogen to get you through a 20- to 22-mile (32 to 35 km) run or a hard interval workout. After a long run or a long interval workout, therefore, your glycogen stores are depleted. It typically takes 24 to 48 hours to completely replenish your glycogen stores. When you do two long or hard workouts in a row, therefore, you risk going into the second workout with partially filled glycogen stores, becoming depleted, and having a bad workout. The frequency with which you can train hard is determined by your recovery rate between workouts, and this will be increased greatly by replenishing your glycogen stores quickly.
Here are strategies you can use to increase your rate of glycogen replenishment.
• Don’t wait. Your body stores glycogen at a faster rate during the first hour after exercise, so have a carbohydrate drink with you when you finish your long runs or other workouts. Bring along some easy-to-digest carbohydrate foods as well. To speed glycogen resynthesis, take in about 1 gram of carbohydrate per kilogram of body weight (a little under half a gram per pound) in the first 15 minutes after the workout, and another gram per kilogram of body weight during each of the following 3 hours.
• Increase your intake of carbohydrate. After a glycogen-depleting workout, increase your carbohydrate intake to approximately 10 grams per kilogram of body weight (4.5 g/lb) during the next 24 hours.
• Eat high-glycemic index foods. The glycemic index of a food is determined by the effect it has on your blood glucose level. High-glycemic index foods cause a large increase in blood glucose levels, whereas low-glycemic index foods have a lesser effect. During the first few hours after a workout, your glycogen stores will be replenished more quickly if you eat high-glycemic index foods, such as potatoes, rice cakes, bread, bagels, and crackers.
Nancy Clark’s Sports Nutrition Guidebook and Endurance Sports Nutrition by Suzanne Girard Eberle are excellent and extensive resources for more information on nutrition for endurance athletes.
The Role of Protein for Marathoners
Conventional wisdom indicates that strength-trained athletes such as weightlifters need lots of extra protein to build muscle but that the protein needs of endurance athletes are the same as for sedentary folks. Over the past 15 years, however, studies have clearly shown that endurance athletes have elevated protein needs. As a marathoner, your body needs protein to repair damaged muscles, to make red blood cells to deliver oxygen to your muscles, to make mitochondria in your muscles to produce energy aerobically, to maintain a strong immune system, and to make enzymes and hormones that keep your body functioning normally.
Sedentary individuals need about.8 to 1.0 gram of protein per kilogram of body weight per day (.35 to.45 g/lb per day). Endurance athletes have elevated protein needs because of their greater wear and tear on muscle tissue and red blood cells, need for more mitochondria, and so on. Several formulas are used for calculating the protein needs of endurance athletes, but a typical guideline is 1.2 to 1.7 grams of protein per kilogram of body weight (.55 to.75 g/lb of body weight) per day (Eberle 2007). Table 2.1 presents daily protein requirements for marathoners.
Chances are that most marathoners meet or exceed their protein requirements through a typical American diet. Runners who are vegetarians or who greatly restrict their meat intake may not meet their protein needs. If you’re a vegetarian, it’s not difficult to meet your protein requirements, but it does require some knowledge and planning.
Eating too much protein can also have negative consequences for your running performance. If you eat too much protein, you may not be consuming enough carbohydrate, so such a diet would reduce your energy levels. Your body would use the excess protein as energy by removing the amino groups and oxidizing the resulting carbon skeleton. This process requires the removal of waste products, which stresses the kidneys and can lead to dehydration.
The Importance of Iron
Iron is vital to running performance. Despite this importance, many runners don’t monitor their iron levels. Even many physicians don’t understand the complete role of iron for endurance athletes.
Iron is necessary for producing hemoglobin in your red blood cells. Oxygen attaches to hemoglobin for transport in your blood to your muscles. If your hemoglobin level is low, less oxygen reaches your muscles, which means your muscles can’t produce as much energy aerobically. The result is that your
O2max and lactate threshold are reduced, and you can’t maintain as fast a pace. In addition, iron is a component of many other substances in the body, such as enzymes in your muscle cells that affect aerobic energy production, so low iron levels may cause low energy levels by altering the composition of these other substances.
For many years, top athletes and coaches have recognized the benefits of a high red blood cell count; this awareness has led to the illegal practices of blood doping and using synthetic erythropoietin (EPO) to increase red blood cell count. EPO is a hormone the body produces naturally that determines the body’s level of red blood cell production. When EPO levels rise through natural means or through injection of synthetic EPO, red blood cell production and hemoglobin levels increase. The result is that the runner can produce more energy aerobically and, therefore, maintain a faster pace.