This is a guest post by Mitchell Vanderkodde
Carbohydrates and Glycogen
If you are a "weekend warrior" or a serious endurance athlete, you are most likely familiar with a phenomenon where your first day back on the road after a rest day is an amazing workout where you have boundless energy and drive. The third day out in a row, you feel sluggish, and your workout suffers. How can you make day three feel as good as day one? For many endurance athletes, the answer could lie in managing your carbohydrate intake and glycogen stores.
Carbohydrates are used by the body in three different ways. They are immediately used as fuel, stored as glycogen, or stored as fat. There are 3 types of carbohydrate: Monosaccharides, Disaccharides, and Polysaccharides. Monosaccharides are simple sugars like fructose and glucose, made up of a single molecule. Disaccharides are a combination of 2 simple sugars like sucrose (a combination of glucose and fructose). Polysaccharides are also known as complex carbs. They are a combination of 3 or more simple sugars, like maltodextrin, a chain of 3 glucose molecules.
Your body cannot store carbohydrates in the same form that it ingests them. It converts them into glycogen through a process known as glycogen synthesis. Glycogen is made up of hundreds, thousands or even tens of thousands of individual glucose molecules in a branched structure, like a tree (unlike complex carbs, which are a single chain of many simple sugars).
Glycogen Stores in the Body
Glycogen is stored by the body in either the liver or the muscles. Glycogen in the liver is easily broken down into single glucose molecules and delivered directly to the blood stream. The blood then delivers the glucose to where it is needed most, usually the brain or muscles. Glycogen that is stored in the muscles is a ready fuel source for that muscle group. Each individual muscle cell has a glycogen store for use by only that cell.
Blood sugar is a measure of the amount of glucose in the blood stream that is available immediately for use by the body as fuel. Blood sugar levels can fluctuate rapidly, so the body uses glycogen stores in the liver and muscles as a buffer against these fluctuations. When blood sugar is too high, the liver will convert the extra glucose in the blood into glycogen for storage. When blood sugar is too low, the liver will convert its stored glycogen back into glucose for use as energy.
How the Body uses Glycogen
Liver glycogen is used primarily during aerobic exercise (running, swimming, biking) and muscle glycogen is used primarily during anaerobic exercise (weight lifting, jumping, sprinting). Glycogen stored in the liver comes from a combination of fructose and glucose, and glycogen stored in the muscles come primarily from glucose.
The Benefits of Replenishing Glycogen Stores
During exercise the body's glycogen stores are depleted. If they are not fully replenished, your next workout will have limited exercise intensity and a shorter time-to-exhaustion. By replenishing glycogen stores, you can eliminate both of these negative effects.
Timing Glycogen Replenishment
The average person has enough stored glycogen for 12-14 hours of normal activity, or 2 hours of moderately intense activity. Several studies have found that after a workout there is a 2 hour "window of opportunity" where your body is able to synthesize glycogen 2-3 times as fast as normal. Your body is even more receptive in the 45 minutes after a workout.
How to Replenish Glycogen Stores
With a smart recovery plan, you can completely replenish glycogen stores within 24 hours after an intense workout. In the 2 hours following a workout, ingest a combination of simple and complex carbs. Throughout the course of the day, eat enough carbs to replenish what was lost during exercise. This can be anywhere from 100 to 500 grams of carbs, depending on the intensity of your workout. By using trial and error, you will be able to figure out what your body needs.
What if I take in too many carbs?
If you ingest more carbs than your body can use or convert into glycogen, it will convert those carbs into fat for long-term storage. Fat is much harder for your body to convert back into glucose for use as energy. This can happen in the short-term as well. If your blood sugar is too high, and the mechanism to convert the glucose into glycogen is overwhelmed, the extra glucose will be converted into fat. The most common way that this happens is by ingesting a large amount of sugary sports drinks immediately following a workout.
Endurance athletes are in a constant struggle to maintain glycogen stores. To stay energized for multiple workouts without a rest day, make sure you are getting enough of the right kind of carbs, at the right time. If you feel your energy levels are low, give your body time to replenish these vital glycogen stores.
About The Author:
Mitchell is an active duty US Marine Helicopter pilot and co-founder of �bloc Nutrition, maker of �bloc Endurance Recovery Drink Mix. You can follow him on Twitter @mitchvk, or check out his website, ablocnutrition.com.