Key Takeaways

  1. Glycogen is a form of carbohydrate that’s stored in your muscles and liver.
  2. Glycogen is the primary source of fuel during exercise, and low glycogen levels decrease your ability to gain strength and muscle.
  3. The best way to maintain high levels of glycogen is to eat a high-carb diet, with around 1 to 3 grams of carbs per pound of body weight or more.

Many people say that you need to eat plenty of carbs to build muscle and strength, and if you don’t, then you’ll be leaving gains on the table.


Here’s how the logic breaks down:

  1. The primary source of fuel for your muscles during intense exercise is a form of carbohydrate stored in the body known as glycogen.
  2. Eating carbs increases your glycogen levels, which allows you to use heavier weights, do more sets, and push yourself harder in workouts.
  3. Using heavier weights, doing more sets, and pushing yourself harder in workouts leads to greater strength and muscle gains over time.

As further evidence of this theory, they’ll point to the plethora of big, lean, strong bodybuilders who eat high-carb diets.

Others object, though.

They claim that you don’t need carbs to build muscle—just adequate protein and calories—and they’ll point to examples of equally big, lean, and strong bodybuilders following low-carb diets to prove their point.    

Who’s right?

Well, here’s the truth:

If you want to build muscle and strength as quickly and efficiently as possible while minimizing fat gain, you want to keep your glycogen levels higher rather than lower, and the only way to do that is to eat a high-carb diet.

In this article, you’re going to learn . . .

  • What muscle glycogen is
  • How, where, and how much much glycogen is stored in the body
  • What glycogen synthesis is
  • How glycogen affects your strength and endurance performance
  • How glycogen affects your body composition
  • How long it takes to deplete your body’s glycogen stores
  • And more.

Let’s get started.

What Is Glycogen?

Glycogen is a form of stored carbohydrate in the body.

It’s formed by linking glucose molecules in chains of about 8 to 12 glucose molecules in length, which are then bonded together to form large lumps, or granules, of over 50,000 glucose molecules.

These glycogen granules are stored along with water and potassium in muscle and liver cells until they need to be broken down and used for energy.

Here’s a drawing of what a glycogen granule looks like:


The coil of multicolored ribbon at the center represents a specialized form of protein that serves as the junction to which all of the strands of glycogen attach.

The glycogen granule is enlarged as more and more strands of glycogen are tacked on to the periphery of this kernel, and it’s shrunken as strands are broken down and used for energy.

Glycogen refers to a large bundle of glucose molecules that are stored primarily in muscle and liver cells.

What Is Glycogen Synthesis?

Glycogen synthesis refers to the creation and storage of new glycogen granules.

To understand how and why glycogen is created, it’s important to understand how your body digests and stores carbohydrate.

After eating a meal, your body breaks down the protein, fat, and carbs into smaller molecules. Protein is broken down into molecules called amino acids, fat is broken down into molecules called triglycerides, and carbs are broken down into molecules of a simple sugar called glucose.

It is possible for the body to convert protein and fat into small amounts of glucose, but this process is very inefficient and only produces enough glucose for basic bodily functions—nowhere near enough to fuel intense weightlifting. It also only revs up when glycogen levels are already low, which is why you must consume carbs to produce a significant amount of glucose.

The body can only store about 4 grams (one teaspoon) of glucose in the blood at any time, and if levels rise too far above this range the excess glucose can damage nerves, blood vessels, and other tissues. If levels stay too high above this range for too long, well, then maybe that’s a sign it’s time for a sit down chat with Wilford Brimley about diabeetus . . .

Anyway, to prevent this from happening, the body uses several mechanisms to dispose of the glucose that it can’t dump into the bloodstream.

The primary way the body disposes of this excess glucose is by packaging it into glycogen granules which can then be safely stowed away in muscle and liver cells.

Then, if the body needs extra energy in the future, it can convert these glycogen granules back into glucose and use them as fuel.

Glycogen synthesis refers to the process of packaging glucose molecules into glycogen granules and storing them in muscle and liver cells.

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Where Is Glycogen Stored?

Glycogen is primarily stored in muscle and liver cells, although trace amounts are also stored in some brain, heart, fat, and kidney cells.

Specifically, glycogen is stored in the liquid inside of cells referred to as cytosol.

Cytosol is a clear liquid comprised of water and various vitamins, minerals, and other substances that gives cells structure, stores nutrients, and helps support chemical reactions within cells.

After being stored in the cytosol, glycogen floats around until it’s broken down into glucose, which is then gobbled up for energy by the mitochondria—the “power plants” of the cell.

Here’s what glycogen looks like under a microscope:

glycogen structure

This is a microscope image of the inside of a liver cell, and the little black dots are granules of glycogen suspended in the cytosol.

Most people can store around 100 grams of glycogen in their livers, and around 500 grams of glycogen in their muscles, although people with more muscle mass and training experience can store considerably more than that.

All in all, most people have the capacity to store around 600 grams of glycogen.

Your body uses the glycogen stored in your liver as an immediate source of energy to fuel your brain and perform other bodily functions throughout the day.

Your muscle glycogen, though, is generally used by whatever muscles are working during exercise. For example, if you’re doing squats, then the glycogen stored in your quadriceps, hamstrings, glutes, and calves will be broken down into glucose to fuel the exercise.

How Glycogen Affects Exercise Performance

The most basic unit of cellular energy is a molecule called adenosine triphosphate (ATP).

For a cell to use ATP, though, it must first break it down into several smaller molecules. This process produces byproducts that are then “recycled” back into ATP to be used again.

The more ATP your cells can store and the faster they can regenerate it, the more energy they can produce and the more work they can do. This is true of every bodily system, including your muscle cells.

When you exercise, your cells require significantly more energy than usual. Thus, your body must generate significantly more ATP to fuel the activity.

For example, during a hard set of sprints your body may generate ATP 1,000 times faster than you do at rest.

So, how does your body kick up energy production to meet these demands?

Your body uses three different processes, known as “energy systems,” to make sure that your muscles always have a steady supply of ATP no matter how hard you train.

These systems, which you can think of as different kinds of engines inside the body, use several different sources of fuel to regenerate ATP including body fat (triglycerides), glycogen, and another molecule called phosphocreatine.

The three energy systems are:

  1. The phosphocreatine system.
  2. The anaerobic system.
  3. The aerobic system.

To understand how glycogen fits into all of this, we need to take a closer look at how each of these systems work.

1. The phosphocreatine system.

Phosphocreatine, also known as creatine-phosphate, is another source of energy stored in muscles.

Muscle can’t store very much phosphocreatine, though, and thus the phosphocreatine system can’t produce as much total energy as the other two (the anaerobic and aerobic systems). The advantage of phosphocreatine as an energy source is that it can be used to regenerate ATP much faster than glucose or triglycerides.

You can think of the phosphocreatine system as an electric motor—it can’t produce much energy, but it can produce it almost immediately.

That’s why the body relies on the phosphocreatine system for brief, intense efforts that last around 10 seconds or less, like a one-rep max bench press.

The downside is that it takes a long time for phosphocreatine to “recharge” after a hard effort, sometimes as long as 5 minutes. (This is why taking creatine improves your performance—it improves the efficiency of your phosphocreatine system).

After about 10 seconds of intense effort, the phosphocreatine system is drained, and your body begins to rely more on the anaerobic system.

2. The anaerobic system.

After around 10 to 20 seconds of effort, the anaerobic energy system starts producing the majority of energy for ATP regeneration.

This is called the “anaerobic system,” because it regenerates ATP without the presence of oxygen. (“An-” meaning “without,” and “aerobic” meaning “associated with oxygen.”) This allows it to produce energy faster, but not as efficiently as the aerobic system.

You can think of the anaerobic system as a typical gasoline internal combustion engine—it can produce a decent amount of energy, but it takes a few seconds to reach full capacity.  

This is also referred to as the “glycolytic system,” because it gets the majority of its energy from glycogen and glucose.

The anaerobic system is primarily used for efforts that last around 20 seconds to 2 minutes, or anything that makes your muscles “burn.” This burning sensation is thanks to metabolic byproducts that build up in your muscles as a result of anaerobic energy production.

Most of your sets in the 8-to-12-rep range in the gym will be powered by your anaerobic system.

3. The aerobic system.

The aerobic system, also called the “oxidative” or “respiratory” system, takes over after about 60 to 120 seconds of effort.

This system can’t produce energy as quickly as the first two, but it can produce it for a much greater length of time and does so much more efficiently.

It also burns through a lot of muscle glycogen when you’re training hard.

You can think of the aerobic system as a diesel engine—it can produce a lot of energy almost indefinitely, but it takes a while to warm up.  

All three of these energy systems are working all of the time, but the contribution of each varies depending on how hard you’re working.

The harder you exercise, the faster your body needs to regenerate ATP, and the more it relies on the first two systems—the phosphocreatine and anaerobic energy systems.

Your aerobic system primarily kicks into gear during extended moderate intensity workouts or when you’re recovering from harder bouts of exercise, like between sets in the gym.

Why does this matter?

Because all three of these energy systems heavily rely on glycogen to power their energy-producing machinery.

If your glycogen levels run low, then these engines start to sputter and fizzle, and your performance will most likely suffer.

If you keep your glycogen levels high, though, providing these engines with plenty of fuel, then you can train harder and for longer.

Let’s take a look at how glycogen affects both strength and endurance in the real world.

Glycogen and Strength

glycogen and strength training

If you’re doing most of your sets in the 4-to-6-rep range, then your sets will typically last around 15 to 20 seconds.

So, if muscle glycogen is primarily used for longer efforts (over 20 seconds or so), then why should it make any difference in your ability to throw around heavy weights?

Two reasons:

First, even though you primarily rely on the phosphocreatine system during short efforts, you still use a fair amount of glycogen, too.

For example, during a 10 second sprint (which imposes a similar demand on the body as a hard set of squats), your muscles get about half their energy from the phosphocreatine system and about half from your anaerobic system.

A good example of the glycogen-depleting effects of strength training comes from a study conducted by scientists at Ball State University.

In the study, they had eight 23-year old resistance trained men perform 6 sets of 6 reps of leg extensions.

The researchers took four tiny samples of muscle tissue from each man’s quadriceps: before the exercises, after 3 sets, after 6 sets, and 2 hours after the workout. Then, they tested the samples to see how much glycogen was stored in their muscle cells before and after training.

Before the study began, the researchers also instructed the men on how many carbs to eat to maximize their muscle glycogen levels before the study, and had them track their food intake for two days before the workout to ensure compliance.

The researchers found that just 6 sets of 6 reps of leg extensions reduced muscle glycogen levels by 23% on average.

This is why low-rep, high weight lifting can still feel harder when you reduce your carbohydrate intake.

Second, between sets, your aerobic system relies heavily on carbohydrate to regenerate ATP. If you don’t have enough glycogen in your muscles to adequately recover between sets, then your performance is going to feel worse and worse the longer your workout drags on.

To be fair, there aren’t many studies on how carbohydrate intake affects strength and muscle gain, and there is some emerging evidence that super low-carb diets might not be as disastrous for these purposes as once believed.

On the other hand, though, the vast majority of studies find that athletes of all stripes perform better when they eat more carbs, and the smart money in sports typically toe the line in this regard, too.

For example, we look at high-level strength athletes for guidance, we also see that they eat a ton of carbs.

Specifically, strength athletes eat around 4 to 6 grams of carbohydrate per kilogram of body weight. For a 200 pound man, that’s a colossal 350 to 550 grams of carbohydrate per day.

The bottom line is that eating a high-carb diet will almost certainly increase your ability to use heavy weights, do more sets, and get stronger and stronger over time.

Glycogen and Endurance

Your body gets about 80 to 85% of its energy from glycogen when you reach around 50 to 85% of your maximum intensity, which encompasses just about every endurance sport.

This is why you see runners snarfing down bananas, bagels, and bars during long runs, and why there’s a massive industry for energy drinks, gels, chews, and other high-carb snacks.

As you near the top end of that intensity range, your body uses exponentially more carbohydrate. That is, if you train at 60% of your maximum intensity, you’ll use more than twice as much glycogen as you do when training at 30% of your maximum intensity.

Thus, the harder you train, the more glycogen you require.

And what happens when you run out of glycogen? A significant uptick in fatigue that prevents you from maintaining your desired pace, or what athletes call “bonking” or “hitting the wall.”

You can prevent this by eating carbs during long workouts and maximizing your glycogen stores by eating a high-carb diet the rest of the time.

Some people think there’s a way to circumvent this problem altogether.

Glycogen isn’t the only source of fuel your body uses during endurance exercise. It also uses a fair amount of body fat.

As you get in better shape, your body becomes more efficient at tapping into its fat stores, so you use less glycogen at the same intensity.

This fact has led some people to believe that you can become “fat adapted.” Follow a low-carb diet, they say, and you’ll teach your body to burn fat instead of carbs, so you don’t need to rely on glycogen and thus don’t need to worry about bonking.

As long as you go slowly, this strategy can more or less work. Putter along at a slow pace, and you can get much of your energy from stored body fat instead of glycogen.

The problem is that if you want to do well at running, cycling, rowing, or any other endurance sport, then you want to go as fast as you can. You don’t want to snail your way through workouts, you want to incrementally go faster and faster, which is going to require more and more glycogen.

This is where the idea of “fat adaptation” falls apart.

When it comes to hard training and racing, people who eat more carbs beat those who eat fewer carbs almost every time.

This is also why every single credible study on nutrition for endurance athletes recommends you eat a high-carb diet if you want to perform at your best.

There’s just no getting around it—every endurance sport requires you to train and race at a pace that uses a massive amount of glycogen. The only way you’ll be able to maintain that pace is if you eat plenty of carbs, and that means no low-carb dieting.

How Glycogen Affects Body Composition

glycogen carbohydrate

When it comes to losing fat and building muscle, carbs (and by extension, glycogen), get a bad rap.

Eat too many carbs, and it will be impossible for you to improve your body composition, or so many claim.

Many also say that carbs don’t help you build muscle, so it would seem they’re all con and no pro.

This is wrong.

You can lose fat and build muscle following a low-carb diet, but you’ll likely make progress as fast or faster if you follow a high-carb diet instead.

Glycogen and Muscle Gain

If you want to build muscle as quickly and efficiently as possible, then you want high muscle glycogen levels for two reasons.

1. Higher glycogen levels let you train harder.

The primary driver of muscle growth is progressive tension overload, which refers to increasing the amount of tension your muscles produce over time, and the most effective way to do this is by progressively increasing the amount of weight that you’re lifting.

The best way to do that, is to get as strong as possible on the big, compound lifts.

If you keep your glycogen levels high, then you’re going to gain strength faster, which means you’re going to gain muscle faster, too.

So, indirectly at least, having higher levels of muscle glycogen should help you build muscle faster.

2. Higher glycogen levels improve recovery.

When it comes to building muscle, how well you can recover from your training is just as important as the workouts themselves.

Low muscle glycogen levels are associated with overtraining, and low-carb diets, which deplete muscle glycogen, increase cortisol and reduce testosterone levels in athletes.

Low-carb diets also reduce insulin levels. In addition to helping store nutrients, insulin also has powerful anti-catabolic properties. This means that insulin decreases the rate at which muscle proteins are broken down, which creates a more anabolic environment conducive to muscle growth.

Maintaining high muscle glycogen levels also improves the post-workout genetic signaling related to muscle growth and repair.

It would be a stretch to say that boosting your muscle glycogen levels directly causes muscle growth, but it probably helps by letting you train harder and bounce back faster from your workouts.

Maintaining higher muscle glycogen levels helps you train with heavier weights and recover faster, which can lead to more muscle growth over time.

Glycogen and Fat Loss

There are all kinds of theories out there on why low-carb diets might help you lose fat faster.

“It keeps your insulin levels lower.”

“It reduces your hunger and cravings.”

“It balances your hormones.”

And every one of these ideas has been categorically and definitively debunked. As long as you maintain an energy deficit, you’ll lose weight regardless of whether you get most of your calories from carbs, protein, or fat.

If you’re a regular around these parts then you’re likely on board with this idea already.

You may have also heard, though, that you need to deplete your glycogen levels to maximize fat loss. Some say this is particularly true once you reach about 15% body fat for men and 25% for women, or around when you start bumping up against stubborn fat.

Once you reach this point, they say, you have to exhaust the glycogen stored in your muscles to force your body to burn fat.

Not only is that not true, doing so can slow your progress.

To improve your body composition, you want to lose fat while maintaining or building muscle mass.

If you cut your carb intake and your glycogen levels, you’ll perform poorly in your workouts, recover slower, and likely lose some strength and muscle mass.

And all three of those things are going to make it harder to get the body you want.

Maintaining higher muscle glycogen levels won’t make you lose more fat, but it will likely help you avoid losing muscle by allowing you to train with heavier weights during your cut.

What Are the Signs of Low Glycogen Levels?

low glycogen

There are a few telltale signs that your muscles are low on glycogen:

  • Your workouts feel awful.

If you’re getting enough sleep and are following a sensible workout routine, and suddenly every weight feels three times heavier than it should, you’re probably low on glycogen.

This is particularly true if you feel worse the longer you’re in the gym. Remember, glycogen is your main source of fuel during weightlifting, so the longer you train without adequate fuel, the harder it’s going to feel.

  • You lose several pounds overnight.

Every gram of muscle glycogen is stored with 3 to 4 grams of water.

A pound is 454 grams, so if you eat 110 grams of carbs (three cups of cooked pasta), you can gain about a pound of total body weight.

On the flipside, if you burn through the majority of your glycogen stores, then you can also lose several pounds in a matter of hours.

While that’s gratifying in the short-term, it can also be a sign that you need to replenish your muscle glycogen.

There are other things that can cause you to lose or gain water weight, but changes in glycogen levels tend to be the big one.

How to Increase Your Glycogen Levels

One large high-carb meal isn’t enough to keep your glycogen levels elevated.

Glycogen is always being broken down and regenerated, which is why you have to maintain a relatively high daily carbohydrate intake.

How high, exactly?

If you’re trying to get stronger and build muscle, then you want to eat around 1 to 3 grams of carbs per pound of body weight per day.

If you want to lose fat, then your carb intake will largely be dictated by how many calories you have left after setting your protein and fat targets. For most people, this will work out to somewhere around 1 to 1.5 grams of carbs per pound of body weight.

If you’re an endurance athlete, then you’re going to burn through far more muscle glycogen than the average gym goer. You may need as much as 4 to 5 grams of carbs per pound of body weight to keep your glycogen levels topped off.

A recent report conducted by Asker Jeukendrup at the University of Birmingham sheds light on how astronomically high your carb needs are during endurance training. Jeukendrup (who’s an accomplished Ironman triathlete), concluded that if you’re training intensely for more than two or three hours at a time, you should try to consume around 90 grams of carbs per hour. That’s about 1 large bagel every 30 minutes.

Luckily you probably aren’t training like that, so you can maintain high glycogen levels with a much lower daily carb intake.

The bottom line, though, is that if you want to maximize your glycogen levels you want to eat as many carbs as you can after ensuring you’re getting enough protein and fat every day.

What Are the Best Foods for Increasing Muscle Glycogen?

foods with glycogen

As glycogen is composed of glucose—a kind of carbohydrate—the best foods for increasing muscle glycogen levels are those that are high in carbs.

Some people resort to refined carbs like breakfast cereal, white bread, and high-carb snacks and desserts like pretzels, Pop-Tarts, and the like to boost their muscle glycogen levels, but this isn’t a great idea.

While any food high in carbs will get the job done, it’s best to focus on whole, minimally processed, nutrient dense sources of carbs for a few reasons:

  1. Food doesn’t just provide just calories, carbs, protein, and fat. It also (should) provides micronutrients like vitamins, minerals, and phytonutrients to support health and vitality.
  2. This kind of diet might work when you’re bulking or extremely active, but it also ingrains eating habits that can become hard to break once you switch back to cutting or become less active.

Instead, here are some of my favorite high-carb foods for topping off glycogen levels:

  • Sweet potatoes
  • White potatoes
  • Bananas
  • Strawberries
  • Grapes
  • Apples
  • Mango
  • Blueberries
  • Oats
  • Barley
  • White and brown rice
  • Gnocchi
  • Dried fruit
  • Whole grain bread
  • Beans

The Bottom Line on Glycogen

Glycogen is a form of stored carbohydrate in the body.

It’s formed by linking glucose molecules in chains, which are then bonded together to form large lumps, or granules, of thousands of glucose molecules.

These glycogen granules are then stored in muscle and liver cells until they’re later broken down and used for energy during exercise.

The body relies on three different processes, or energy systems, to produce energy during exercise:

  1. The phosphocreatine system.
  2. The anaerobic system.
  3. The aerobic system.

All three of these systems directly or indirectly rely on glycogen to produce energy, and when glycogen levels run low they aren’t able to function at full capacity.

This is why low glycogen levels reduce performance in almost every sport.

When it comes to strength training and other high-intensity sports, glycogen is used to recover between sets (or intervals), which is why heavy, low-rep weightlifting still feels harder when your muscle glycogen levels are low.

When it comes to endurance training, up to 85% of your energy during exercise comes from glycogen, which is why if you run out of muscle glycogen you simply won’t be able to go as fast or as far.

And when it comes to improving your body composition, maintaining higher muscle glycogen levels will help you use heavier weights, which is going to help you maintain your muscle while cutting.

The most common signs of low muscle glycogen levels are . . .

  • Your workouts feel awful despite getting enough sleep and following a sensible workout routine.
  • You lose several pounds overnight, which is a sign that your glycogen levels have dropped.

The best way to maintain high glycogen levels is to follow a high-carb diet.

Specifically . . .

  • If you’re bulking you want to aim for 1 to 3 grams of carbs per pound of body weight per day.
  • If you’re cutting you want to aim for 1 to 1.5 grams of carbs per pound of body weight per day.
  • If you’re participating in endurance sports you want to aim for 2 to 5 grams of carbs per pound of body weight per day (depending on how much you train).

A good rule of thumb is that if you’re training hard in any sport, you generally want to eat as many carbs as you can after ensuring you’re getting enough protein and fat every day.

The best foods for maintaining high muscle glycogen levels are going to be high in carbs and relatively low in protein and fat, which includes things like potatoes, grains, beans, fruits, and some high-carb veggies.

The bottom line is that if you want to have more productive cuts, gain more muscle and strength on your bulks, and perform better at any sport, then you want to maintain higher muscle glycogen levels, not lower. And that means following a high-carb diet.

If you want to learn how to set up a diet that will help you maintain high glycogen levels, then check out these articles:

How to Make the “If It Fits Your Macros” Diet Work For You

A Simple and Accurate Macronutrient Calculator (and How to Use It)

How to Know Exactly How Many Carbs You Should Eat

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What’s your take on glycogen? Have anything else to share? Let me know in the comments below!