Glycogen is a term often used in endurance sports.
But what is glycogen and why should it matter to you?
Read on to find out what glycogen is, how to manage glycogen, and why glycogen is crucial to improve your athletic performance.
What is glycogen?
In simple terms, glycogen is a form of glucose that your body stores for fast energy, primarily in the muscles and liver.
To fill your glycogen stores, you must consume carbohydrates.
Whenever you consume carbohydrates, your body digests them into glucose. The body uses glucose for energy and transforms extra glucose into glycogen to be used for energy later. This process is called glycogen synthesis or glycogenesis.
As your body's main source of energy, glycogen obviously takes an important role to sustain your body functions, which includes both physical and mental activity.
When the body depletes its glycogen stores, you will run out of energy. As an endurance athlete, this is something you should definitely keep in mind!
How much glycogen is stored in the body?
Your body can store about 100 grams of glycogen in the liver.
It can also store glycogen in the muscles, about 1 to 2% of the muscle mass, which on average means around 400 grams.
Glycogen is also stored in very small amounts in other tissues, such as brain, kidneys, and even blood cells.
Depending on your muscle mass and ability to store glycogen, your body may store from 500 to 600 grams of glycogen.
When will the body use glycogen?
When glucose is not available, your body will use liver glycogen to manage glucose levels in your blood. That's because only liver glycogen can be delivered to other parts of your body.
On the other hand, muscle glycogen can only be used to fuel the activity of the specific muscle it is stored in.
Also, once the intensity of your exercise reaches a certain threshold, approximately 70% of your VO2 max, glycogen will become your body's preferred source of energy.
If you want to increase your VO2 max, check out our training plan!
Your body can store around 500 grams of glycogen in the muscles and liver to be used as fast energy when glucose is not available.
Glycogen during exercise
During exercise, especially intense endurance exercise, your body needs a lot of energy. As the intensity of your exercise increases and you approach your VO2 max, your metabolism goes up, while your digestion goes down.
This means that glycogen becomes increasingly important, as your body will rely on its glycogen stores to keep running.
Unfortunately, your body will deplete its glycogen stores in approximately 2 hours of intense exercise. Once that happens, you will bonk or hit a wall or, in simplest terms, not be able to continue with your physical activity.
For this reason, endurance athletes pay special attention to glycogen and use several strategies to keep glycogen stores as full as possible.
To slow down glycogen consumption, you must provide your body with glucose.
Since your glycogen stores are directly linked to your carbohydrate intake, most of these strategies revolve around nutrition.
Let's look into it.
How to manage glycogen with nutrition?
If you want to keep your glycogen stores as full as possible, you need to intake a sufficient amount of carbohydrates.
But simply intaking large amounts of carbohydrates is not the way. You must also respect your body's ability to digest carbohydrates and the natural limits of your glycogen stores. While both can be improved with training, there are limits to that as well.
To properly manage your glycogen stores, you should consume carbohydrates before, during, and after exercise.
Glycogen stores before exercise
Ideally, you want to begin your endurance exercise with your glycogen stores fully loaded.
To achieve that, athletes use a strategy named carbohydrate loading. Basically, this involves eating plenty of carbohydrates in the days (or hours) leading to the physical activity.
While there are several detailed strategies out there how to best perform carbohydrate loading, you can follow these simple guidelines.
- Eat primarily fast-acting, high glycemic index carbohydrates.
- Avoid eating too much dietary fiber, as it may cause digestive issues.
- Deplete your glycogen stores with a training session before commencing carbohydrate loading.
- Take at least one full day to properly fill your glycogen stores, but if that is not an option, eat a breakfast filled with fast-acting carbohydrates.
- Consume an energy gel or an isotonic drink 30 minutes before physical activity.
Fill your glycogen stores before exercise with carbohydrate loading.
Glycogen stores during exercise
During intense exercise, you want to preserve your glycogen stores as long as possible.
To achieve this, you need to sustain a sufficient intake of carbohydrates. The amount required depends on the intensity of your exercise and your physical preparation, but a rule of thumb is 60 to 90 grams of carbohydrates per hour.
The ideal source of carbohydrates is a combination of two simple sugars, glucose and fructose.
Glucose is your body's main source of energy, has a high glycemic index, and will be quickly absorbed into your system, significantly slowing down your glycogen consumption.
Fructose has a low glycemic index, but in combination with glucose it allows you to use both carbohydrate transporters in your body, which improves absorption and is the only reasonable way to absorb 90 grams of carbohydrates per hour.
Slow down glycogen depletion during exercise with energy gels and isotonic drinks.
Glycogen stores after exercise
After intense exercise that lasts several hours, even if you sustained proper nutrition during exercise, your body's glycogen stores will be close to depleted.
You should refill your glycogen stores as soon as possible.
Refilling your glycogen stores is part of proper recovery, which also includes an intake of protein to feed your muscles and an intake of minerals aka electrolytes to rehydrate.
While you could achieve this with regular food, proper recovery requires the intake of these nutrients within 30 minutes after exercise, which is why athletes most often use recovery drinks.
Recovery drinks are extremely efficient, as they provide:
- the correct amount and concentration of fast-acting carbohydrates,
- a concentrated source of protein for efficient muscle recovery,
- minerals to induce proper rehydration and allow your body to function.
Use a recovery drink to start refilling your glycogen stores immediately after workout.
Negative effects of glycogen depletion
The main negative effect of glycogen depletion is running out of energy. Whether you are an endurance athlete or working at the office, your body needs energy to sustain physical and mental activity.
Glycogen, or its related processes glycogenolysis and glycogen synthesis, is directly linked to stress. As stress increases, glycogen decreases. And as glycogen decreases, stress increases.
There are several negative effects of long-term stress, which is something that affects several endurance athletes.
- Weakened immune system leads to illness and injuries.
- Illness and injuries prevent you from training and progressing.
- This prevents you from realizing your full athletic potential.
Since depleting glycogen stores is a regular process in endurance sports, stress is a constant factor you should be mindful of. Additionally, you may suffer from stress because of your mental processes. In this case, check out these useful tips from a sports psychologist.
Depleting your glycogen stores will make you run out of energy and increase stress levels.
Glycogen is glucose stored as energy in your muscles and liver.
During intense exercise, you will deplete your glycogen stores within 2 hours, which has negative effects, such as running out of energy and increasing stress.
To fill glycogen stores and slow down glycogen consumption, you should intake carbohydrates before, during, and after exercise.
The best way to sustain a sufficient carbohydrate intake, especially during exercise, is by using dietary supplements, such as energy gels and isotonic drinks. After exercise, we recommend using a recovery drink.