ISSA SN Chapter 19: Glycogen Loading

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Chapter Goals:

  • Describe and define the terms that relate to loading glycogen. 
  • Know how the loading of glycogen works in our bodies.
  • Know the methods that exist for glycogen loading.
  • Be able to find the athlete types that benefit the most from these strategies of loading glycogen.


The skeletal muscles use carbs as their main source of energy when we are doing high intensity exercise and competitions to keep those high level contractions consistent. Our dietary carbs can be used for energy and storage as glycogen molecules in the muscles and liver. These energy stores are used when they are needed. They are broken down into glucose molecules and used then as energy in the same form the carb would originally be used before storage. The amount stored depends on the level of fitness, the training level, and the diet’s composition. As the training is increased, carbs become a more dominant energy source for the muscles. This will be true for strength athletes as much as it is for endurance athletes. And this supply of glycogen is more limited than that of the stores in fat. For this, we must ensure that our athletes have their glycogen stores at the highest level possible. It is also important to remember that when the stores in glycogen are depleted, we have to resort to using the amino acids in the muscle tissues for energy and glucose manufacturing. So, building up the stores is ideal, if only to limit that from happening. 

Why “Glycogen” Loading (Supercompensation) for Athletes?

Carb loading and carb supercompensation have been used for many publications. The term glycogen loading seems to be a bit more correct and utilized in recent science. It also works to show that we are, in fact, building up, is the stores of glycogen and not simple carbs. It is done by loading carbs in certain ways, so it is not entirely wrong also to say carb loading. 

Glycogen Loading Science

During glycogen depletion, catabolism works on the glycogen molecules to turn them into their usable form as glucose. And then this again will be catalyzed to make the energy we need. 

Anabolism comes into play to synthesize the glycogen from the glucose molecules being put together. Glycogen synthase is one of the main enzymes that work through this anabolic process.

Glycogen Loading Origins

Many decades ago, it was discovered that when the glycogen in our body runs out, fatigue worsens, and there is a noticeable reduction in the quality of work and performance. Then, it was discovered that when the stores are depleted, they can hold more glycogen the next time when we replenish them well. Now, the method has transformed to pack more than the normal amounts of glycogen at one time in the stores. This allowed the endurance runners to run much longer without hitting the wall, as they call it. 

These experiments on the different diet effects on the body were conducted in Scandinavia in the 1960s. We also discovered that the muscle content of glycogen was higher than normal when a diet followed normal mixed nutrients. 

This all led us to the modern glycogen loading that we briefly discussed before this section. 

So, glycogen loading will primarily be for endurance sports competitions. These are the ones that will need the greatest storage of glycogen possible due to the extremely long competition times.

We start this loading around six day before competing. The athlete tapers down their exercise at this point for a few days to focus on upping the glycogen content in the body. 

Glycogen – Loading (supercompensation) Approaches Overview

The approaches can follow two different phases:

The glycogen loading depletion phase is when we deplete the stores in the body through manipulation of the diet, restriction of calories, or an increase in the duration of training so that we can use all of it.

The glycogen replenishment phase is when the training intensity and duration are lowered, and carbs content is increased drastically. This can also have rest days and exercise taper days leading up to the competition.

Traditional Glycogen Loading (Carbohydrate Loading) Approach

It is referred to as the traditional, classic, or original approach. It is effective for most long distance endurance athletes, but the trend recently has been for less grueling approaches to carb loading.

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First, the glycogen depletion phase usually lasts three days and starts 6 or 7 days before the athletic event. The diet is super low for these three days in the content of carbohydrates. This can be as low as 100 grams daily or about 15 to 20 percent of the total range of calories daily. Thus, the diet will be high in both protein and fats and in proportions that work best for the athlete. It is obvious to see why this approach is somewhat tough and unpleasant and partner it with the training at a high or moderate intensity level to assist this depletion in glycogen stores. The importance here is to try and still maintain the proper caloric intake levels, even with these severe dietary changes. 

Second, the glycogen loading phase is usually three days and starts right after the depletion stage. Here, we will have a high amount of carbs in the realm of 60 – 70 percent of the daily calories. This can be around 400 – 700 grams every day. There should also be adequate protein and lipid content to make the diet work. The exercise is tapered and reduced to a low level with a possible rest day in there also before the athletic event. Hydration is well maintained. 

There are many unpleasant potential side effects to look at also. It is a tough way to deplete the glycogen stores.

Modified Glycogen Loading Approaches

This is an alternative to the above approach. It attempts to overcome unpleasant side effects with the more traditional approach. 

First, the glycogen depletion phase has the athlete eliminating or modifying the depletion phase approach. The afternoon or evening training session is followed by low carb meals or snacks, and then the fasting during sleep and when you wake up and eat, you begin with loading carbs in the meal. If the energy levels are still high, you deplete them with another training session and then start the loading. It is somewhat similar to the former traditional approach, but it is done more so on a meal to meal basis instead of days of it. This makes it more bearable for athletes. 

Second, the glycogen loading phase has been seen to be effective when done for only one or two days. The reserves should be efficient enough to increase the level of glycogen stored in the body by a solid amount. 3 – 4 days would be even better when implemented. The high carb diets again range around 60 – 70 percent in carbs and the intake of protein and lipids should make up for that and get the appropriate protein levels. 

The longer endurance event athletes will likely benefit more from having part of that traditional approach in there with the depletion phase, but maybe to the level of this approach. It really helps those stores increase more. 

International Olympic Committee 200 Glycogen Loading Approach

Some of the crucial points made in this collection of studies for the recommendations for an endurance athlete are:

Tough training bouts did one week before the event are beneficial. 

In the following three days, there should be moderate intensity training and well balanced mixed diets employed with 45 – 50 percent of carbs.

In the three days after that, the training should taper off and the carb content should rise to 70 percent of calories, which will promote the loading of glycogen in the body.

This stays similar and basically follows the traditional plan.

ISSA SN Chapter 19: Glycogen Loading 4
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Tyler Read - Certified Personal Trainer with PTPioneer

Tyler Read

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