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Carbohydrates and Glycogen
for the Endurance Athlete

By Anne Guzman, PCG Nutritionist

Peaks Coaching Group

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Anne Guzman writes:

As endurance athletes, it is imperative that we pay attention to our body’s nutritional needs. One of the biggest mistakes we make is to undermine our training efforts by not fueling the body properly to get the gains from the hard work we do in training. Why spend so much time and effort working so diligently to hit all your wattages and heart rates and then not show up on the line properly fueled to enable your body to perform its best? Training and nutrition, when properly followed on a consistent basis, create the best performances.

Carbohydrates are an important fuel during exercise. Carbohydrate-rich foods include grains, potatoes, sweet potatoes, and rice, which are mostly starches and fiber and are often referred to as complex carbohydrates. Fruits and vegetables are also carbohydrates. Sugar is also a carbohydrate, consumed too often in the Western world. Sugar is what is referred to as a simple carbohydrate. Complex and simple are referring to the number of monosaccharides in a carbohydrate; one monosaccharide is the basic unit of a carbohydrate. An example of this would be glucose, fructose, and galactose. A starch is a polysaccharide, which is 3-9 monosaccharides combined.


Carbohydrates are important fuel for endurance athletes

Carbohydrates are athletes’ largest and most efficient source of fuel. Unfortunately for us, unlike fat we have a limited storage capacity for carbohydrates. The stored form of carbohydrates is called glycogen. Glycogen is the limiting fuel for exercise. It is needed to fuel muscles, supply glucose to the brain, and burn fat.

Glycogen is most quickly depleted with higher intensity exercise such as Vo2 intervals or long, hard efforts. You can completely deplete your glycogen stores in a hard ninety-minute effort.  Glycogen can fuel up to two hours of moderate to intense exercise. When it comes to this type of exercise, the rule of thumb is eat early and often. Don’t wait until you start feeling depleted and tired to start fueling your body.

In order to perform optimally, we need to be sure we have adequate stores of glycogen available for training and recovery from training sessions and races. Without proper amounts of carbohydrates in our diet, we will face glycogen depletion. You may have already encountered the symptoms of glycogen depletion during training, which can include the following:

  • heavy legs
  • loss of focus
  • normal training seems harder than usual
  • dizziness and sluggishness
  • overall fatigue
  • you have to stop your session altogether because you just feel empty
  • irritability and exhaustion
  • inability to be explosive; you seem to have only one pace left

Symptoms can come on over several days of consecutive training with inadequate nutrition, or they can come on during one intense or long exercise session with inadequate nutrition.

Vincenzo Nibali

Vincenzo Nibali couldn't make this attack without the right fuel in his tank.

How can you stay on top of your carbohydrate needs to be sure you have adequate glycogen available for proper training day after day? Here are some things that may help you.

If you train with a power meter, you’ll know how many calories you burn in a training session. By applying the following information, you will quickly be able to tell when you have depleted your glycogen stores.

Muscle glycogen in the body is approximately 350g, or between 1,400 and 1,800 calories. Liver glycogen is approximately 80-100g, around 320-400 calories. Therefore the body can store up to approximately 2200 calories in glycogen and as few as 1700.This will typically vary depending on your size.

Knowing this, you can look at your power meter and know that if you burn 2,000 calories on a good weekend training ride, you have likely depleted your glycogen stores if you started with your body fully fueled from the previous day’s training. If you started with your tank half empty, you could be feeling the symptoms of glycogen depletion halfway through your ride unless you started eating early and often. This is what we call bonking.

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This knowledge can serve you very well. If you start to realize the caloric expenditure for training rides, you can be sure to fuel while you ride to stay on top of your daily caloric needs and glycogen needs. Remember, the longer you train the less time you have to eat your calories off the bike. Playing catch-up can get very difficult off the bike when you’re riding 3-4 hour rides and burning over 2,000 calories. Start eating while you’re training to be sure to meet your caloric needs. This will also keep you from arriving home so hungry after a ride that you end up overeating. When we allow ourselves to get this hungry, we often will eat anything that comes into sight! Not an intelligent idea.

Research indicates that you can fill up your glycogen stores with twenty-four hours of rest and proper nutrition. Ideally, before an event you would give yourself forty-eight hours of rest and proper nutrition and try to super-compensate, possibly getting a few more hundred calories of glycogen storage.

So what can you do to keep the stores topped up? For starters, it is important that your daily caloric intake is made up of 60% carbohydrates, 15-20% protein, and 20-25% fats. Build a nutrition plan based on this premise. Carbohydrates are the main fuel source for endurance athletes.

On top of this there are some basic principles you can follow leading up to a race or good training session. For every hour that you allow for digestion pre-event, consume just under ½ gram carbohydrates per pound, or 1g/kg.  For example, four hours before an event, consume 2g carbohydrates per pound or 4 g/kg. If you weigh 130 pounds (2g), you should consume 260g carbohydrates, which could be a bagel with peanut butter or a smoothie (2 cups rice milk, 1 banana, ½ cup dry oats, 1 cup orange juice, 1 cup frozen strawberries).

You can also have a carbohydrate drink to sip on as the event approaches. A sports gel thirty minutes prior to training or racing with 500 ml of water is another option. Always consume gels with water.

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To prevent glycogen levels from dropping to critically low levels, ingestion of 1.0-1.2 grams per minute of easily digestible carbohydrate is recommended during exercise, especially after a period of 60-90 minutes of endurance activity (Jeukendrup, 2004). Ingestion of a readily available carbohydrate can permit glycogen sparing and allow for intensity and duration of the activity to be optimized. Therefore, during your event or training, consume 60-70 grams of carbohydrate per hour. This could be in the form of combined sports drink and training food, or food alone with water and electrolytes. This alone can change your performance a lot if it isn’t something you’re currently practicing.

Examples of 60-70 grams of carbohydrates would include one eLoad gel plus one package of Honey Stinger Chews, 1.5 packet of eLoad Endurance Formula in your bottle plus one eLoad Energy Gel, or four Fig Newton cookies plus one serving of eLoad endurance drink.

Once off the bike, start consuming carbohydrates within the first hour. This is very important to glycogen replenishment. In the first post-exercise hour the rate of glycogen storage in the body is almost twice as high due to the high levels of glycogen synthase present, which helps to convert glucose to glycogen. This means quicker recovery for you and is referred to as your “recovery window.”

High-glycemic, easily-digestible carbohydrates such as potatoes and fruit juice would be good examples of food choices post workout. You should aim to eat 1.2g of carbohydrates per kilogram of body weight for up to 4-5 hours post race or hard training session to be sure you have topped up your glycogen stores for the next race or training session. Also include 6-10 grams of protein in your post-recovery meals. For example, if you weigh 75 kilograms (165 pounds), 75x1.2=90, which means you should eat 90 grams of carbohydrates every hour for 4-5 hours after your race. A good snack containing 90 grams of carbohydrates is a small 100% whole wheat bagel plus one medium banana plus eight ounces fat-free chocolate milk.

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Try these methods and notice the difference in your ability to do hard training sessions repeatedly in the same week, as well as in your ability to recover during stage races and long events such as triathlons. We endurance athletes often aim to be super lean, but be sure not to sacrifice your performance in place of good, solid nutritional needs. It’s better to perform strong and finish strong than to be too lean and not have the energy stores to outperform the competition.

Creating a proper nutrition plan is vital to being a top performing athlete. It is important to know how many calories you consume and burn to stay on top of your energy needs and weight throughout different parts of the season. Consider hiring a professional to help you get started with a plan and discover the difference proper nutrition can make in your performance.

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