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Understanding Glycogen, Your Body’s High-Performance Fuel Addie dog eyes a plate full of glycogen-rich french fries. Photo by David Roche.

Understanding Glycogen, Your Body’s High-Performance Fuel

Glycogen fuels performance, and manipulating it properly can make you stronger.

David Roche October 10th, 2017

Put 100 runners around a pre-race dinner table, and they won’t agree on much. Training talk may cause shouting matches; shoe talk could cause friends to come to blows over terms like “drop” and “stack height.” But one thing most would agree on is what to eat—a big pasta buffet.

Pasta has earned its vaunted place at pre-race meals everywhere because of its impact on glycogen. You have probably heard the term “glycogen” bandied about before, and you may have even used it yourself when ordering your pre-race meal.

I know that when I order at restaurants, I am implicitly saying, “I’ll have the large glycogen pizza, please, with a side of glycogen breadsticks.” But what is glycogen, and how can you use it to avoid the dreaded bonk?

 

The Basics

Glycogen is a branched polymer of glucose stored in the liver and muscles that acts as a fuel source for exercise. Glycogen metabolism is the process by which these stored carbohydrates are used as fuel, involving many enzymes with chemical compositions that fill a quarter of a page. While the glycogen-to-fuel process is complex enough to fuel many PhD dissertations, the basic takeaway is that excess carbohydrates are stored as glycogen in the liver and muscles, turning pasta into performance.

Among other things, the breakdown of glycogen is used in ATP synthesis, which is essentially how energy transfer happens in cells. Even though glycogen only accounts for a minimal amount of total stored energy in the body, lower-burning fat takes too long to go through the same process to fuel sustained moderate exercise, so at around 55 to 65 percent of VO2 max for most athletes, glycogen stores become essential to maintain performance levels (though exact intensity depends on many athlete-specific factors).

Think of fat and carbohydrate burning on a spectrum, with high-intensity efforts involving mostly carbohydrates and low-intensity efforts involving mostly fat. Both energy sources are important for running.

According to cycling expert Dr. Iñigo San Millán, at race pace, most athletes will burn two to three grams of carbohydrate per minute. Even at lower intensities, most athletes will burn one to two grams of carbohydrate a minute (though this rate can be adjusted with training). Most athletes store 300 to 500 grams of glycogen when fully fueled, equating to about 90 to 120 minutes of intense exercise.

Glycogen burns rapidly but is refilled at a drip, usually replenishing at a rate of two to five percent per hour after exercise. Empty glycogen stores can take a full day or more to restore.

Three ways glycogen is important for endurance athletes.

1. Glycogen fuels performance for most trail runners.

If your training and racing goes beyond low-level aerobic exercise, you will need to use glycogen to perform at your peak potential. According to a paper in Medicine and Science in Sports and Exercise, chronically low glycogen stores in athletes can cause fatigue and even induce a “catabolic” state involving muscle breakdown by requiring the body to rely on proteins and amino acids for fuel. That is one reason why low energy availability over time may contribute to a reduction in performance, and even overtraining syndrome.

Related: 4 Natural Energy-Gel Alternatives

2. Glycogen re-synthesis can improve recovery.

As outlined by an article in the Journal of Sports Science and Medicine, because glycogen helps muscles recover and avoid cannibalizing themselves for fuel after high-intensity exercise, replenishing glycogen can preserve muscles and accelerate recovery. Topping off glycogen stores will help you get ready for another run sooner.

3. Training in a glycogen-depleted state can enhance some training adaptations and improve aerobic efficiency.

While the body generally needs glycogen to perform at a high level, it can be trained to use its glycogen stores more strategically. An article in the journal Sports Nutrition outlines how running in a glycogen-depleted state can enhance markers for adaptation to training and make the body better at burning fat. Some top ultrarunners like Zach Bitter and Jeff Browning take it one step further, using a low carbohydrate high fat (LCHF) diet to train their body to burn mostly fat at relatively fast paces. However, LCHF diets are complex and controversial, and should be undertaken solely for training purposes when preparing for low-intensity events, at the advice of an expert.

 

How should you maximize glycogen fueling in your own training?

1. Train with adequate glycogen stores by eating carbohydrates in your daily diet.

Don’t overthink things. Just prioritize a balanced diet rich in healthy carbohydrates like whole grains, along with plenty of good fat and rich protein. Since glycogen levels take many hours to fill up, what you ate yesterday is often more important than what you eat the morning of. Avoid food restriction and eat guided by hunger.

2. After runs, prioritize replenishing glycogen through carbohydrate intake.

After exercise, the body is aching to top off glycogen stores. Chocolate milk is often cited as a good post-run drink due to its mix of carbohydrates, protein and fat. While it’s hard to think of a more delightful nutrition suggestion, any similarly carbohydrate-rich food will work.

3. During runs, replenish glycogen as you go.

As glycogen levels drop, so, too, does performance for most athletes. For runs long enough to begin burning stored glycogen (usually 60 to 90 minutes or longer), practice refueling as you go. For most athletes, 200 to 300 calories per hour of mostly carbohydrates—like gels or sports drink—is a safe bet, adjusting for body type and background.

4. You can’t replenish glycogen as fast as you can burn it, so temper your effort level.

In events 90 to 120 minutes and below, if you start with full glycogen stores, you can pretty much go as hard as you’d like and avoid low-glycogen bonking. Over that, you need to pace yourself to avoid running on empty.

As a thought experiment, imagine that a typical athlete has about 360 grams of carbohydrates stored as glycogen, and can replenish 60 grams per hour while burning 180 grams per hour. With no carbs, the athlete goes two hours until bonking. Even with adequate carbs, the athlete will bonk in less than three hours. So the key is to reduce the amount of carbohydrates burned per hour by reducing intensity so the body can burn more fat. In other words, pace yourself to achieve the optimal fat-to-carbohydrate burn rate to avoid bonking.

My general glycogen-related pacing guideline is: you can go hard in events less than two hours, moderately hard in events two to three-and-a-half hours (glycogen can mostly be replenished at strong efforts), moderate for events three and a half to five hours (when fat burning becomes more important), easy/moderate up to eight hours and easy and conversational in anything over that.

5. Do some runs (including some longer runs) in a glycogen-depleted state.

You can use glycogen depletion as a tool to enhance training adaptations. An approach I use with some of the ultra athletes I coach is to do every third long run at very low intensity in a glycogen depleted state (no carbohydrates since the evening before), doing back-to-back long runs every month (even with normal fueling, this type of schedule causes glycogen depletion naturally) and doing short doubles on one or two workout days most weeks. However, to keep it simple, you can just do your daily morning run without breakfast occasionally. (Note: Dr. Stacy Sims, author of the book “Roar,” indicates that glycogen depletion may be less useful—and possibly detrimental—for some female athletes due to hormonal shifts. Very few of the professional female athletes I coach aim for glycogen depletion in a structured way, though will sometimes do back-to-back long runs and doubles for other reasons.)

 

David Roche runs for HOKA One One and NATHAN, and works with runners of all abilities through his coaching service, Some Work, All Play.

Leave A Comment

24 Comments on "Understanding Glycogen, Your Body’s High-Performance Fuel"

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Rudiger
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What a bunch of 1980’s era bro science. I don’t need a side of diabetes with my 10K PR.

David Roche
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Thank you for comment Rudiger! Nutrition is complex and this article focuses on the general concept of glycogen rather than specifics, like what constitutes a healthy carbohydrate, absorption rates, and lower carbohydrate approaches. The takeaway of research is usually to eat a balanced diet focused on whole foods (with the caveat that different things work for everyone, and the big goal is to find what is healthiest for you in the context of your running and life goals).

Adam
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I think that nowadays, any such article on sports nutrition, especially one about carbs/glycogen, should more deeply address the keto issue and crowd.

Sara
Guest

Reliance on glycogen for athletic performance certainly isn’t bro science. While there are a few nutrition researchers who promote low carbohydrate diets, the position of the ACSM and Academy of Nutrition and Dietetics is that carbohydrates play a key role in performance. While absolute values vary between athletes, and intake should be periodized based on training load, the benefits of carbohydrate intake to athletic performance are clear.

Sal
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Just like nutrition is a complex subject, so is running. Fueling for athletes who prefer distances that can be completed in less than 1 hour most likely don’t have to concern themselves with refueling other than eating a balanced diet. For those athletes who train and compete in distances longer than 90 minutes, nutrition becomes more important. Every person is different and has to do their own experimentation, but refueling within certain intervals with some form of carbohydrate is necessary. It may be old science, but it’s still valid.

David Roche
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Thank you Sara and Sal for your valuable contributions. You are both amazing!

RB Q
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If your goal is a 10K you don’t have to care about what David wrote in his article. But what he has written is not some bro science hack job. It is actually a good summary of the role glycogen plays while running long distance races.

Sir Thrusty
Guest

Interesting point Rudiger. I hope you are fueling properly when attempting your 10k PR, after all David said that you begin burning stored glycogen during runs of 60 to 90 minutes or longer.

Mark MacAskill
Guest
Interesting article, David. “However, to keep it simple, you can just do your daily morning run without breakfast occasionally.” I assume that means no calories during some of those runs as well? As an early morning runner with an extremely volatile stomach, I run six days a week without breakfast beforehand. But I often take in calories during runs longer than 10 miles, especially if the runs involve mountains. Because of my stomach issues, I’m especially interested in being cautious with my glycogen stores during ultras and burning fat more efficiently. I never know when I’ll be able to eat… Read more »
David Roche
Guest
Great question Mark! Exactly–most people will be in glycogen-depleted state for morning runs, especially if dinner is earlier and/or lower carb. So those AM runs can get many of the adaptations, even if they aren’t 10 miles or greater. There is an interesting study on cyclists that had a low-carb dinner, followed by an AM spin prior to refueling and training later in the day. That group had 9% greater adaptations to training than the control group. However, the applicability of that study to running is not necessarily direct. So to answer the question, yes to the no carbs during… Read more »
Mark MacAskill
Guest

Fascinating. Thanks again!

David Roche
Guest

WOOHOO! All this stuff is immensely complicated and debated, so I try to write the articles to apply as broadly as possible. But every individual physiology varies a bit, and different things may work for you!

Adam
Guest

What do you mean by adaption? How was that measured? Why might that not translate to running?

Adam
Guest

Back in my ultra days, I would regularly run 25-30mi, and as ~45mi (pre GPS days) on 0 calories (water and electrolytes). That would include dropping some 7:00 miles at the end. Now, still, I’m unlikely to take any calories unless I’m going 3+ hours, or perhaps 2 with intensity, perhaps longer on the bike.

Every body is different. I don’t recommend that much to people I coach, but I do encourage some 0 cal training.

Mark
Guest

Used to train/race on a diet that was 80% carbs. Pre-race dinner was always pasta. During race fuel was Snickers bars. Can’t tell you how many times on the way to the track it was a Pepsi and fun sized snickers, then 3-4 miles of intense intervals. Used to carry pure glucose tablets for the last 20 minutes of a race if I was bonking. Seemed to work for me–3:58:50 for Pikes Peak round trip.

David Roche
Guest

80% carbs is incredibly high! Amazing! Mark, your experience and amazing results show the wide range of approaches that can lead to great success, and how there is truly no one-size-fits-all approach that works for everyone. So cool!

Adam
Guest

80% may have actually been a bit low for those of us who were triathletes and took up Pritikin in the 80s 😀

David M
Guest
David, I occasionally will have a Gel during a run lasting 60 to 75 mins., or finish a run of a similar duration with a G2 Gatorade, especially if the run involved a high level of intensity or perspiration. Based on your article, it sounds like I can skip the gel, and probably even the Sports drinks on most of my runs. But I admit, the carbs do seem to make me feel better. But what happens to them if the muscles don’t need them, & liver stores are full? Are those carbs. stored in the body as fat?
David Roche
Guest
Thank you for your comment David! You asked a question that gets into some really complicated areas of nutrition science. At a basic level, unused glycogen does get stored as fat, though if you’re running 60 to 75 minutes, it’s unlikely you’re at risk of that immediately afterward (though if you work really hard at eating the rest of the day, you can gain weight at almost any level of running training). For your everyday run, you probably don’t need to think too much about fueling during or immediately after. Just focusing on healthy daily nutrition should be plenty! You… Read more »
Peter
Guest

I trained for several months on low carb/high fat diet, including long runs w/ zero carb intake, all to enhance fat metabolism. The day before a 50K race ate a normal carb load and consumed moderate levels of carbs during race. Managed to take 2nd in my age group — my best finish ever in a 50K.

Brian
Guest

As an ultra runner and registered dietitian, you did a great job summarizing glycogens role in exercising and backing it up with studies. Eating carbs as part of a balanced diet will not give you diabetes, so 80’s bro.

David Roche
Guest

Thank you so much Brian, this means the world to me. Your expertise is extremely valuable!

Mats S
Guest

Just a bit of warning here: Train first for distance taking in adequate energy before you do your long runs with little or no carbs. Also, don’t do low carb long runs everytime. They tax you hard and progress could be less than optimum or even going backward.

Andrew
Guest

Interesting read, David. Thanks for sharing your expertise and shedding light on the subject. I wonder, if I were to eat breakfast before a run, but try to keep it carb-less/low carb, what would I be eating? Other than bacon and eggs, which tend to feel quite heavy, I can’t think of any other minimal-carb breakfast foods that would sit well in my stomach. I’d appreciate your suggestions.

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