Tuesday, April 19, 2011

Carbohydrates and Glycogen For The Endurance Athlete

Peaks Coaching Group Anne Guzman Nutrition

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 of your wattages and heart rates and then not show up on the line PROPERLY FUELED to allow your body to perform its best? Training AND Nutrition create the best performances when properly followed on a consistent basis.

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 which is 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 to 9 monosaccharides combined.

As athletes carbohydrates are our 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 90 minute effort.  Glycogen can fuel up to 2 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 to feel depleted and tired to start fueling your body.

In order for endurance athletes 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 the diet we will face glycogen depletion. You may have encountered the symptoms of glycogen depletion during training which can include;
  • Heavy legs
  • Loss of focus
  • Normal training seems harder than usual
  • Dizziness, sluggishness
  • Overall fatigue
  • You just have to stop your session altogether because you just feel “empty”
  • Irritable, exhausted
  • Inability to be explosive as you seem to only have one pace left
Symptoms can come on over several days of consecutive training with inadequate nutrition, or can come on during one intense or long exercise session with inadequate nutrition. 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 will 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 1,400-1,800 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 low as 1700. Typically this will vary depending on your size.

Knowing this, you can look at your power meter and know that if you burn 2000 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 a half empty tank, you could be feeling the symptoms of glycogen depletion half way through your ride unless you started eating early and often. THIS IS WHAT WE CALL BONKING!!!!

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 are riding 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 are riding for 3-4 hour rides and burning over 2000 calories. Start eating while you’re training to be sure to meet your caloric needs. Also this will stop you from arriving home so hungry after a ride that you end up over eating. Often when we allow ourselves to get this hungry we will eat anything that comes into eye sight!! Not an intelligent idea!

Research indicates that you can fill your glycogen stores back up with 24 hours of rest and proper nutrition. Ideally before an event you would give yourself 48hours 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 premises. 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. 

Example: 4hrs before would be 2g carbohydrates per lb or 4g/kg
130lb (2g)=260g carbohydrates   
260g = 1 bagel with peanut butter, smoothie (2cups rice milk, 1 banana, 1/2cup dry oats, 1cup   orange juice, 1 cup frozen strawberries)