Let’s Talk About Glycogen! (and Tapering and Carb Loading)

I’m tapering for the Mississippi Blues Marathon, and in a few days I’ll start carb loading.  We do this mostly because of one fancy word: glycogen. I’ve heard the word bandied about but I wondered Do I really know what it means?  And am I doing the right things with regard to glycogen?  Thank goodness for the internet.

Here’s what I’ve figured out…

(Disclaimer:  I am not a doctor or a nutritionist.  This post synthesizes some information I found on the internet but I’d love to hear from others on their knowledge about glycogen, carb loading, and tapering.  The human body is constantly being studied, and in 20 years sugary, trans fat-laden frosting might be the new health food we are all gulping down before a race.)

What is Glycogen?

First stop: Wikipedia.

Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals and fungi. The polysaccharide structure represents the main storage form of glucose in the body.

In humans, glycogen is made and stored primarily in the cells of the liver and the muscles hydrated with three or four parts of water. Glycogen functions as the secondary long-term energy storage, with the primary energy stores being fats held in adipose tissue. Muscle glycogen is converted into glucose by muscle cells, and liver glycogen converts to glucose for use throughout the body including the central nervous system.

Glycogen is a complex carbohydrate, but not every carb you eat gets stored as glycogen.   Skeletal muscles can store about 400 grams of glycogen.  If you don’t use the carbs you eat as fuel or store the carbs as glycogen (i.e., if you hit your max storage), the carbs get stored as fat.  As you eat excess calories, the fat accumulates inside your adipose cells causing the cells to expand and increase in size.

Why Do We Hear About Glycogen Related to Marathons and Other Endurance Sports?

Again, Wikipedia:

Long-distance athletes, such as marathon runners, cross-country skiers, and cyclists, often experience glycogen depletion, where almost all of the athlete’s glycogen stores are depleted after long periods of exertion without enough energy consumption. This phenomenon is referred to as “hitting the wall”.

Runner’s World further explains,

When you eat a bowl of spaghetti, most of the carbs are stored as glycogen in your muscles and liver. Glycogen is your body’s most easily accessible form of energy, but it’s not the only source… During a half or full marathon you burn both glycogen and fat. But the latter is not as efficient, which means your body has to work harder to convert it into fuel.

It elaborates on this glycogen vs. fat concept in another article,

When you run, your body burns a mixture of carbohydrate and fat. Your body stores carbohydrate as glycogen in your muscles and liver (the fitter you are the more you store), which is broken down to glucose as needed. The harder you run, the more carbohydrate you use. As your glycogen stores become progressively more depleted during a run, your body conserves what’s left by relying more on fat. Because fat is about 15 percent less efficient than carbohydrate as an energy source, when you run low on glycogen you slow down. You can therefore improve your training and race performance by managing your glycogen stores.

A few summary points so that we are all on the same page.

  • All exercise burns both carbs and fat.  During intense exercise, the body takes more from carbs relative to fat because the fat calories are less accessible.  At lower heart rates, the body uses fewer total calories and also uses a lower ratio of carbs to fat (this is sometimes referred to as the “fat burning zone” which is a bit of a misnomer)
  • But whether you are running fast or slow and regardless of your heart rate, your  body is going to be using lots of glycogen to fuel a marathon, and if you don’t have enough, you can get super fatigued.
  • Also, in case you were wondering, fat loss on your body (i.e., trimming down) does not appear to be directly related to which you are burning — carbs or fat.  Or which you are eating, for that matter.

Does Having More Stored Glycogen Make Me Run Faster?

The consensus seems to be that increasing glycogen stores improves endurance.  It doesn’t necessarily help you run faster at mile 5 or 10 or 15; it enables you go to longer at that pace.  But when you’re talking about a marathon, where most of us do get quite tired before the finish line, endurance can translate into a faster time.

How Do We Keep Ourselves From Depleting All Our Glycogen During a Race aka Hitting the Wall?

Well that’s a big question.  Let’s take it in smaller pieces.

Can Nutrition Replenish Our Glycogen Stores During Our Race

You might be saying to yourself Welp, I’ll load up on the Gatorade and candy corn, and I will have more glucose than my body can handle.  No wall hitting here.

Think again.  Runners Connect reports,

Your body has a limited supply of glycogen available to fuel your working muscles. Most research has shown that you can run about 2 hours at marathon intensity before you run out of glycogen… Unfortunately, while helpful in extending glycogen stores, simply eating on the run won’t entirely replace all the glycogen you burn. Midrace fueling is limited by how quickly your digestive system can deliver the glycogen to your bloodstream and, under the duress of marathon racing, the stomach is not very efficient.

I’ve found this echoed elsewhere.  Like Wikipedia:

[D]uring exercise, carbohydrates with the highest possible rate of conversion to blood glucose (high glycemic index) are ingested continuously. The best possible outcome of this strategy replaces about 35% of glucose consumed at heart rates above about 80% of maximum.

So race nutrition is important (not just for carb-burning but also for big-deal things like electrolytes), but it won’t be able to totally prevent bonking.

Well, What if We Just Practice Running Without Glycogen in Our Muscles?  Won’t We Get Stronger For Race Day? 

Some sources recommend “glycogen-depleted” or “fasted” endurance training.  This concept relies on a “train low, race high” approach.  The theory is that the body becomes conditioned to use fuel more efficiently and to use fatty acids as fuel, rather than carbohydrates.  Although the OSU study discussed below indicates that you can adapt to burn more fat instead of carbs by consuming a high-fat and low-carb diet, the evidence to support fasted endurance training is mixed.

Runners Connect reports,

Similar studies have made it clear that occasional fasting before exercise can improve glycogen storage and endurance performance.

However, other studies have gone further and tested the effects of training with low glycogen levels for more than one run or for extended periods of time. The research concludes that extended carbohydrate depletion impairs performance and does not enhance fat utilization.

The research makes a strong case that occasional long runs in a fasted state will improve glycogen storage and fat utilization, but extended training or multiple long runs in the fasted state will impair performance and does not provide further benefits to fat utilization.

Runner’s World also has some words of caution about “training low”:

Renowned exercise physiologist Bengt Saltin, Ph.D., and colleagues at the University of Copenhagen have suggested that allowing muscle glycogen levels to become depleted may lead to improvements in athletes’ adaptation to training. Studies have found that exercising with low muscle glycogen levels leads to greater activation of genes involved with several types of beneficial training adaptations. One specific adaptation that is enhanced by glycogen depletion is the ability of the body to store glycogen. Depletion of muscle glycogen leads to increased activity of glycogen synthase, which is the enzyme that increases glycogen storage. So, rather than consistently topping up your stores and using a carbohydrate drink during training, there may be a benefit to allowing your glycogen tank to run low during some workouts.

Many high-mileage runners have been putting this approach into practice for years by doing long runs with little or no carbohydrate intake, and running twice per day with the tank already moderately depleted going into the second workout of the day. By tapering training and carbohydrate loading for races, they “train low” and “race high” in terms of their glycogen stores.

The “train low” concept is relatively untested and much is yet to be learned about how much depletion is required, how often to do it, and how to minimize the risks of delayed recovery from training and immune system suppression associated with carbohydrate depletion. Therefore, use moderation if you are going to try it. Every one to two weeks, do a moderately long run without taking in carbs during the run and gradually increase the length or intensity of the run. If you feel much more tired than usual towards the end of the run you have probably overdone it.

I do some unintentional “training low” when I don’t get up early enough before a workout to eat…  So maybe I’m adapting?

What if We Deplete Our Stores During Our Training Runs?  Will That Teach Our Muscles to Increase Glycogen Storage?

Runner’s World gives a little history lesson:

Studies in the 1960s showed that athletes can substantially increase their muscle glycogen stores by doing a long workout seven days before a competition, then eating a low-carbohydrate diet for three days, followed by a high-carbohydrate diet (70-80 percent of calories from carbohydrate) for the three days preceding the race. The long run depletes the body’s glycogen stores and the three days of low carbohydrate intake keeps them low, which signals the body to store as much glycogen as possible. The downside of the carbohydrate depletion phase is irritability, weakness (which is not great psychologically before a key race) and immune system suppression.

Later studies showed that you can increase your glycogen stores to similar levels without the depletion run and low-carbohydrate phase by tapering training and eating a high-carbohydrate diet during the last three days before a race.

Oh, So Carb Load?  We’ve Heard of That!  We Love That!

Does Everyone Agree About That We Need to Eat Lots of Carbs to Have Enough Glycogen?  

Of course not.  Let me just get this one article front and center now.

According to an article from Ohio State University:

Muscle glycogen was discovered in the 1960s to be a critical energy source for athletes, which led to decades of emphasis on high-carb diets to support energy needs during intense exercise.

BUT! (You knew there was a “BUT”).

According to the OSU study, elite endurance athletes who ate very few carbohydrates as part of their regular diets burned more than twice as much fat as high-carb athletes during maximum exertion and prolonged exercise.  Moreover, despite their low intake of carbs, these fat-burning athletes had normal muscle glycogen levels — the storage form of carbohydrates — at rest. They also broke down roughly the same level of glycogen as the high-carb runners during the long run, and synthesized the same amount of glycogen in their muscles during recovery as the high-carb athletes.  The researchers had not expected that!  They hypothesized that the athletes in the study, who had already been following a low-carb diet for had least six months, had trained their bodies to support glycogen levels without eating a bunch of carbs.

Importantly, this study did not look at performance.  It doesn’t say “X person ran faster/longer/better on a low-carb diet than they did on a high-carb diet.”  (Is there a published article on that?)  It did find that people who ate fewer carbs still had glycogen in their muscles, and that eating more fat and less carbs seems to have made that fat energy more accessible.

There are many folks out there who run and who don’t eat a ton of carbs.  If this is interesting to you and you want to try adapting to a lower-carb diet while running marathons, here is a nice little intro piece from No Meat Athlete.

Moving on…

OK, Assuming We Buy in to the Carb Loading Concept, How Do We Properly Carb Load Before a Race?

  • Runner’s World has the following recommendation: For a marathon on Sunday, you would do a moderate depletion run (e.g., one hour with 20 minutes at marathon race pace) on Wednesday morning and eat low carbs throughout the day, then after a light run on Thursday morning start carbohydrate loading. The one-day depletion provides a strong stimulus to your body to store glycogen while minimizing the side effects.
  • For the two to three days before your race, 85 to 95 percent of your calories should come from carbs, according to Runner’s World.  Greatist cites a study suggesting that a little less is optimal: carbs should comprise between 63 and 81 percent of total calories.
  • Runner’s World recommends eating about four grams of carbs for every pound of body weight (for a 150 lb person that is 2,400 cals of carbs).
    • I am no expert but I’d caution against eating that many calories.  If I eat that much before a race, especially carbs, I feel completely gross, weighed down, and bloated. Yes, even if the calories come from “good carbs” and not processed foods.
    • I try to keep my calorie intake about the same as normal (1,500-2,000 cals) but increase my percentage of fruits, rice, beans, and pasta and decrease my percentage of nuts and eggs.
  • To help bump up your carb intake, avoid high-fat foods such as creamy sauces, cheese, butter, and oils that will fill you up and provide lots of non-carb calories.
  • Don’t increase your fiber significantly beyond what you eat normally.  Doing so can disrupt the belly.  Carb loading is a nice time to catch up with those white carbs and juices you might be missing in your normal, healthy, 2016 life.  Get nostalgic (white bread! orange juice! childhood!).
  • Run Your BQ gives some other practical tips for getting those carbs.
  • In any event, some weight gain can happen with proper carb loading.  Runner’s World says,

You should expect to gain a couple of pounds when you carbo-load because your body stores 2.6 grams of water for every gram of glycogen. The added weight is unavoidable, and the stored water may help prevent dehydration during the race.

What Does Tapering Have to Do with Glycogen?

Reducing your running before a race will allow the glycogen you consume from carbohydrates to accumulate in your muscles.

But tapering does other great things too.  From Runner’s World:

Tapering allows muscle glycogen stores to return to peak levels. Metabolic enzymes, antioxidants, and various hormones, depleted during training, return to their optimal ranges. Muscle and connective tissues repair and strengthen. And, the body’s immune system improves dramatically too. In short, tapering allows your body to prepare for peak performance.

Experts suggest a one to three week taper.  Runner’s World suggest cutting your weekly mileage volume by 20 to 30 percent each week from your highest volume week for three weeks.  Sounds like a lot of math to me.  I usually do my final long run two weeks before the race and then just chill until the race, doing some easy runs, yoga, pilates, lifting, etc. as my body desires.  (Runner’s World says not to do any lower body work during the taper period.  Agree to disagree, for now.)  I usually do not do any meaningful workouts for four days before the marathon.  This article from MarathonTraining.com has some nice tips for the taper.

Here is something else I didn’t know,  also from Runner’s World:

During the taper, it is most important to remember this: physiological adaptations to training take a minimum of six weeks. Therefore, training hard during the final two to three weeks before your marathon is not going to improve your performance.

So my last ditch Orangetheory workout tomorrow won’t make me stronger for the race?  Bummer!

How Do We Reload Our Glycogen Levels After a Race?

Runner’s World advises,

Glycogen reloading is greatly enhanced after exercise and remains moderately higher for about six hours. Take advantage of this window of opportunity by taking in carbs through eating and drinking as soon as practical after a hard run or race.

The first 30 minutes is the most effective period for replenishing your glycogen stores, followed by the next 30 minutes, the following hour and so on. Consuming 50 to 100 grams of carbohydrate within 30 minutes of finishing your run, and another 50 to 100 grams within the next hour will kick-start the replenishment process. Glycogen replenishment and overall recovery is also enhanced by taking in a moderate amount of protein (e.g. 15 to 25 grams) with the carbohydrate. Foods with a high glycemic index are best during the first hour after exercise and should be followed by a high carbohydrate meal within five to six hours of completing the run.

I wrote this post to educate myself but I hope it has been informative for you too.  Who has some more info, questions, stories, and tips about glycogen, carb loading, and tapering?  Please let me know in the comments!  



3 thoughts on “Let’s Talk About Glycogen! (and Tapering and Carb Loading)

  1. Pingback: Mississippi Blues Marathon 2016 Recap and Review (Marathon 15, State 10-Mississippi) | athlettuce

  2. Pingback: Up Next in March 2016… | athlettuce

  3. Pingback: Last Week of Asheville Marathon Training | athlettuce

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