Glycogen is made from several connected glucose molecules and is your body's primary and preferred source of energy.

Glycogen is stored in your liver and muscles and comes from carbohydrates in the foods you eat and drink. Most of the carbohydrates we eat are converted to glucose, our main source of energy. When the body doesn't need fuel, the glucose molecules are linked together in chains of eight to 12 glucose units which form a glycogen molecule.

Most glycogen is found in the muscles and the liver. The amount of glycogen stored in these cells can vary depending on how active you are, how much energy you burn at rest , and the types of food you eat.

Glycogen stored in muscle is primarily used by the muscles themselves, while those stored in the liver are distributed throughout the body—mainly to the brain and spinal cord. Glycogen should not be confused with the hormone glucagon, which is also important in carbohydrate metabolism and blood glucose control.

Your body converts glucose to glycogen through a process called glycogenesis. During this process, your body breaks down glycogen in a process called glycogenolysis that the body can then use. Various enzymes help with this process.

At any given time, there is a set amount of glucose in the blood. When the level begins to decline—either because you have not eaten or are burning glucose during exercise—insulin levels will also drop. When this happens, an enzyme called glycogen phosphorylase starts breaking glycogen down to supply the body with glucose.

Glucose derived from liver glycogen becomes the body's primary energy source. Short bursts of energy use glycogen, whether that's during a sprint or lifting a heavy weight. This is why having a carbohydrate-rich pre-workout drink can help you exercise longer and recover quicker.

Similarly, you should be eating a post-workout snack with sufficient carbohydrates to replenish glycogen stores, preferably balanced with at least 20 grams of protein.

This is why you may feel mentally sluggish and experience "brain fog" when you don't consume enough carbs. What you eat and how much you move around also influence glycogen production. The effects are especially acute if you're following a low-carb diet , where the primary source of glucose synthesis—carbohydrate—is suddenly restricted.

When first starting a low-carb diet, your body's glycogen stores can be severely depleted and you may experience symptoms like fatigue and mental dullness. Additionally, any amount of weight loss can have the same effect on glycogen stores. Initially, you may experience a rapid drop in weight.

After a period of time, your weight may plateau and possibly even increase. The phenomenon is partly due to the composition of glycogen, which also contains water. As such, rapid depletion of glycogen at the onset of the diet triggers the loss of water weight.

Over time, glycogen stores are renewed and the water weight begins to return. When this happens, weight loss may stall or plateau. Gains experienced in the beginning come from water loss, not fat loss, and are only temporary. Fat loss can continue despite the short-term plateau effect.

For endurance athletes who burn a lot of calories in a couple of hours, the amount of stored glucose can be an impediment. When these athletes run out of glycogen, their performance almost immediately begins to suffer—a state commonly described as "hitting the wall.

If you're undertaking a strenuous exercise routine, there are several strategies endurance athletes use to avoid decreased performance you may find helpful:.

Glycogen is supplied through the carbohydrates in your diet and is used to power your brain and athletic pursuits as well as many other bodily functions. Restoring glycogen after you exercise is a vital part of the recovery process.

Eating enough carbs for your goals and activity level is essential for success. Glycogen does not make you fat. The only thing that can increase body fat is consuming more calories than you burn while not using them to build muscle.

Consuming more calories than you burn is also necessary for building muscle mass. Excess glycogen is stored in the liver where it may be used later for energy. Your muscles are also a storage area for glycogen. Excess glucose above this can be converted into triglycerides which are stored in your fat cells.

Note that any type of excess calories, no matter which macronutrient they come from can lead to body fat gain. There is nothing inherent in carbs, glucose, or glycogen that increase your risk of gaining body fat.

When your glycogen stores are depleted through exercise or due to not consuming enough carbs, you will feel fatigued, sluggish, and perhaps experience mood and sleep disturbances. Murray B, Rosenbloom C.

Fundamentals of glycogen metabolism for coaches and athletes. Nutr Rev. Goyal MS, Raichle ME. Glucose requirements of the developing human brain. J Pediatr Gastroenterol Nutr. doi: D'anci KE, Watts KL, Kanarek RB, Taylor HA. Low-carbohydrate weight-loss diets. Effects on cognition and mood.

Winwood-Smith HS, Franklin CE, White CR. Low-carbohydrate diet induces metabolic depression: A possible mechanism to conserve glycogen. Am J Physiol Regul Integr Comp Physiol. Adeva-Andany M, Gonzalez-Lucan M, Donapetry-Garcia C. Glycogen is essentially a long chain of glucose sugar molecules that are attached end to end with an occasional cross linkage.

Figure 1 shows the basic structure of glycogen. Note that the glucose molecules are attached end to end. A glycogen molecule would consist of thousands of these linkages with occasional cross linkages as illustrated in Figure 2. Although the liver has a higher concentration of glycogen than muscle there is more glycogen stored in muscle tissue because muscle tissue is more abundant than liver tissue.

The average person would store about grams of glycogen in their muscles and grams in their liver. Since 1 gram of carbohydrate contains 4 Calories, the body stores approximately Calories in the form of muscle and liver glycogen.

The glycogen stored in muscle and liver comes from dietary carbohydrates if sufficient quantities of dietary carbohydrates are consumed. Once ingested, the carbohydrates that we eat are digested to simple sugars by pancreatic and salivary amylase.

Sugars other than glucose are largely converted to glucose in the small intestine. Some sugars like fructose the primary sugar in fruits when consumed in significant amounts the amount varies but for fructose it is typically 50g or more per meal may enter the bloodstream in their native form and must be converted to glucose by the liver.

Once the sugars reach the bloodstream they are driven into the liver and muscle cells by the action of the hormone insulin.

Insulin also activates the enzyme glycogen synthase, which synthesizes glycogen by adding one glucose at a time to the glycogen chain. When muscle and liver glycogen levels are replenished, the excess glucose is burned preferentially to fat. In other words, consuming excess carbohydrates more than is needed to replenish glycogen stores shifts the body from burning primarily fats at rest to consuming primarily carbohydrates at rest.

This process is also activated by insulin. If caloric intake is in excess of caloric need, the excess carbohydrates will be stored as fat.

The body cannot use glycogen as a source of energy in its storage form. In order to derive energy from glycogen the body must liberate individual glucose molecules to use for energy production. This process is accomplished by activating the enzyme glycogen phosphorylase. Glycogen phosphorylase removes glucose units, one at a time, from the glycogen chain.

Glycogen phosphorylase is activated automatically when muscles begin to contract. When muscles contract, the calcium concentration inside of the muscle cell increases.

Calcium converts the inactive form of glycogen phosphorylase to a more active form of glycogen phosphorylase. This provides glucose to fuel the muscular activity.

If the exercise continues for any length of time the body begins to produce hormones that also activate glycogen phosphorylase. Some of the hormones are glucagon, epinephrine and norepinephrine. These hormones activate both muscle and liver glycogen phosphorylase. Although the liver is metabolically active, most of the glucose that is produced is released into the bloodstream.

The glucose that is released by skeletal muscles is trapped inside of the muscle cell and cannot contribute to blood sugar. The liver release of glucose from glycogen helps to maintain blood sugar levels during exercise.

Some of the blood sugar is used as a source of fuel by the nervous system and some is taken up by skeletal muscle as an alternate source of glucose to fuel muscle contraction.

Muscle glycogen may be the most important energy substrate during exercise. At the beginning of all types of exercise and for the entire duration of high intensity exercise, muscle glycogen serves as the primary metabolic energy substrate 1Powers and Howley, Because muscle glycogen concentration influences endurance performance 2 Conlee, and may also affect maximum power output 3 Heigenhauser, Sutton and Jones, , manipulating glycogen stores is a potentially important consideration for a wide variety of athletes.

In Ahlborg and colleagues 4 began to demonstrate the relationship between diet and muscle glycogen concentrations. Figure 3 below demonstrates the results of the study. When subjects consumed a low carbohydrate diet glycogen concentrations decreased then rebounded to double baseline concentration on a high carbohydrate diet.

This effect increased glycogen storage ability following glycogen depletion when consuming a high carbohydrate diet is referred to as glycogen supercompensation.

Glycogen supercompensation is different than glycogen compensation. Glycogen compensation is a normal response to exercise and refers to the process of replacing muscle glycogen to normal levels following exercise. Supercompensation occurs when glycogen concentrations are replaced to supra-physiological levels much greater than normal.

Since the glucose that is produced from muscle glycogen does not leave the muscle cell, glycogen is only depleted in muscles that are exercised 6 Hultman, The amount and type of carbohydrate ingestion that will maximize glycogen resynthesis has been the subject of numerous research studies.

Costil et al. Blom et al 8 showed that glycogen resynthesis was maximal when subjects consumed 25 grams of glucose per hour. Keizer et al. Based on these studies it appears that 25 grams of carbohydrates per hour grams per day is sufficient for a maximal rate of glycogen resynthesis.

A study by Roberts et al. The simple sugar fructose the primary sugar found in fruits is effective at replenishing liver but not muscle glycogen This is because muscle tissue lacks the enzyme necessary to convert fructose to glucose.

Therefore fruit is a bad carbohydrate choice for carbohydrate loading or supercompensation. One of the earliest studies on the effects of muscle glycogen on endurance was conducted in by Ahlborg and colleagues 4. In this now classic study, he demonstrated a correlation between initial muscle glycogen concentration in the vastus lateralis muscle of the quadriceps and exercise endurance using a continuous bicycle ergometer protocol.

Since this study there have been numerous studies validating this effect see Conlee, for a review. In another classic study Bergstrom and associates 12 studied the effects of altering carbohydrate consumption for 3 days on exercise to exhaustion.

The researchers had the same subjects consume a mixed diet, a high low carbohydrate diet, and a high carbohydrate diet for three days. After each three-day period glycogen concentrations were measured and the subjects exercised to exhaustion on a bicycle ergometer. The results are summarized in Figure 3.

and performance Performance is also plotted on the y axis in minutes. from only 3 days of dietary manipulations. The order of the treatments was mixed diet, followed by high fat – high protein and finally high carbohydrate. Not only did the high carbohydrate diet replace the carbohydrate stores that were depleted by the high fat – high protein diet, but it actually increased glycogen concentrations over baseline levels.

Bergstrom and colleagues concluded that the ability to sustain prolonged exercise depends on muscle glycogen concentration. The myriad of studies that followed firmly established the theory that sustaining performance in endurance events lasting longer than one hour is strongly dependent upon maintaining glycogen concentrations and that fatigue during these events is probably due to glycogen depletion 2.

Although glycogen depletion does not cause fatigue during high power events 13 , glycogen depletion has been shown to reduce the ability to produce a high power output. A standard power test involves pedaling as fast as possible against a fixed resistance for 30 seconds. Conlee 4 speculates that this reduction in power output occurs because some fibers are no longer capable of contributing because they are almost completely devoid of glycogen.

Since there are fewer fibers available to contribute, power output is reduced. Since every gram of glycogen is stored with approximately 3 grams of water 13 a doubling of glycogen stores due to glycogen supercompensation is likely to increase the apparent size of muscles.

Since exercise upregulates the body’s ability to store glycogen and bodybuilders have more muscle mass than the average person, we might expect that a bodybuilder stores considerably more than the grams of glycogen mentioned earlier as an average value for normal adults.

For the sake of argument let’s assume that a bodybuilder is storing grams not an unreasonable amount of muscle glycogen. By carbohydrate depletion and supercompensation to twice that level again, not unreasonable it would be possible to add grams of glycogen plus grams of water to the bodybuilder’s muscle tissue.

This amounts to a 7. Therefore a bodybuilder can potentially gain a significant amount of apparent mass with successful glycogen supercompensation. Beginning a typical 3-day depletion, 3 day loading supercompensation cycle just prior to a competition may not be the best strategy for an endurance athlete.

This is because glycogen depletion requires vigorous exercise and most endurance athletes refrain from vigorous exercise during the final week prior to a competition to ensure adequate recovery.

Fortunately glycogen levels stay elevated for at least 3 days following a glycogen supercompensation cycle 5. This allows the athlete to start the cycle 9 days prior to competition and still allow 6 days of recovery before the event. A typical glycogen supercompensation cycle would look something like this:.

The vigorous exercise should use the same muscles that are going to be used during the competition since it is these muscles that will be depleted and supercompensated. In other words, if you are a runner you carbohydrate deplete by running. If you are a cyclist you carbohydrate deplete by cycling.

Most of the carbohydrate consumption on day 1 of the high carbohydrate phase should be simple sugars and intake should not exceed 25 grams per hour or 75 grams every three hours.

Carbohydrates should be consumed at least every three hours so that continual glycogen synthesis is occurring. If, as Conlee speculated 4 , some muscle fibers are completely glycogen depleted by high power performances and subsequently are incapable of contributing, one might speculate that power athletes could benefit by glycogen supercompensation.

For many athletes, however, actual performance during competition would not be enhanced by supraphysiological levels of glycogen. For weightlifters, for example, performance is related to the ability to produce force and not the ability to maintain force output over time. Although glycogen loading can delay the reduction in force output during repeated maximal contractions 14 , no study to date has shown that maximal force production can be enhanced by supraphysiological concentrations of glycogen.

The same logic applies to jumpers and throwers. For high power events lasting less than 10 seconds m sprint the majority of the energy comes from stored Adenosine Triphosphate and Creatine Phosphate with little contribution from carbohydrates Brooks and Fahey For high power events lasting longer than 2 minutes performance is limited by the cardiovascular system

The study reviewed is Subcellular Localization- and Fibre Type-Dependent Utilization of Muscle Glycogen During Heavy Resistance Exercise in Elite Power and Olympic Weightlifters by Hokken et al. The last decade or so has been tough for carbohydrates.

Back in the s, things were much simpler; dietary fat was vilified for its purported impact on blood lipids and cardiovascular disease risk, and high-carb diets were heavily promoted for the general population and athletes alike.

A key focus of the sports nutrition field was focused on glycogen replenishment strategies, as carbs were universally acknowledged as the primary fuel for moderate-to-high intensity exercise. More recently, low-carbohydrate diets have become more and more common among athletes, and specifically among strength and physique athletes.

Even extremely low-carb diets, such as ketogenic and carnivore diets, have been embraced by some. One thing that has facilitated the resurgence of low-carb diets for lifters has been a body of literature indicating that a single resistance training session fails to fully deplete muscle glycogen levels.

This line of thinking overlooks a critical detail about glycogen storage: glycogen particles are stored in multiple distinct compartments within muscle, and different storage depots have different impacts on muscle function and fatigue 6.

Total muscle glycogen can be divided up into intramyofibrillar glycogen located within the myofibrils, mostly near the z-line , intermyofibrillar glycogen located between the myofibrils , and subsarcolemmal glycogen located just beneath the sarcolemma.

It appears that intramyofibrillar glycogen most directly relates to muscular fatigue development via impairment of calcium release from sarcoplasmic reticula. So, the current study aimed to assess the effects of high-volume resistance exercise on the utilization of glycogen from various storage depots in competitive male powerlifters and Olympic weightlifters.

While only intermyofibrillar glycogen dropped substantially in type 1 muscle fibers, all three storage depots were markedly reduced in type 2 fibers, and a decent number of type 2 fibers had almost full depletion of intramyofibrillar glycogen after exercise.

We never want to place too much confidence in a small collection of studies, but the evidence for the importance of localized glycogen depletion is mounting.

Read on to get more details about what these results mean for carbohydrate intake in lifters. The presently reviewed study sought to quantify the effects of a high-volume resistance training session on localized depletion of distinct muscle glycogen storage depots in type 1 and type 2 muscle fibers.

The researchers hypothesized that high-volume resistance exercise would lead to different patterns of localized glycogen depletion in specific storage depots and fiber types.

Based on the introduction section, it seems safe to infer that they were specifically expecting to see some functionally relevant depletion of the intramyofibrillar storage depot, which has been linked to acute muscular fatigue in previous research.

Based on their self-reported 1RMs and years of training experience, it sounds like these participants were pretty solid lifters. Their relevant demographic data are presented in Table 1. In many of the previous glycogen depletion studies in this area, the researchers look at estimates of whole-muscle glycogen levels via biochemical analysis of tissue homogenate.

They basically take a sample of muscle tissue, grind it up, and see what the glycogen concentration of the ground up muscle tissue is. This precludes them from distinguishing between type 1 and type 2 fibers, let alone distinguishing between distinct glycogen storage depots.

In the presently reviewed study, the researchers used this method to take a quick look at overall glycogen depletion, but they also used a more advanced method with microscopic examination of intact samples of muscle tissue quantitative transmission electron microscopy , which allows them to look at differences between muscle fiber types and specific depots of glycogen storage.

On the manipulation side, the researchers were specifically focused on determining how resistance training impacted glycogen depletion patterns.

Participants arrived for testing after an overnight fast and were provided a standardized pre-exercise meal minutes prior to a standardized bout of resistance training. The exercise session began with some light warmups, followed by three exercises that were intended to target the lower body musculature since glycogen levels were being assessed using vastus lateralis tissue samples.

The workout consisted of back squats done in accordance with International Powerlifting Federation standards , deficit deadlifts from a 10cm platform, and dumbbell split squats with the rear foot elevated on a standard bench.

A quick overview of the exact exercises, set and repetition schemes, and approximate loads is presented in Table 2. During their four sets of split squats, participants were instructed to aim for an RPE of about on a point reps in reserve-based RPE scale while completing 12 reps per set.

Participants rested for minutes between sets of squats and deadlifts, and minutes between sets of split squats.

In order to assess changes in muscle glycogen, muscle biopsies were obtained about minutes prior to the onset of exercise and immediately minutes after finishing the exercise session.

In terms of outcome variables, the researchers were primarily interested in assessing total muscle glycogen depletion, fiber-specific glycogen depletion, and location-specific depletion of glycogen from the distinct storage depots within muscle tissue intramyofibrillar glycogen, intermyofibrillar glycogen, and subsarcolemmal.

As one would expect, muscle glycogen concentrations decreased and muscle lactate concentrations increased in response to the training bout.

Using the more intensive method of glycogen quantification transmission electron microscopy , they were also able to look at distinct, localized glycogen storage depots in type 1 and type 2 muscle fibers.

The relative percentage of total muscle glycogen contained within each localized storage depot intramyofibrillar, intermyofibrillar, and subsarcolemmal is presented below in Table 3.

In response to the exercise bout, glycogen stores were depleted in a non-uniform manner. When expressed as a percentage in Table 2, the non-uniformity is hard to see, but it becomes more apparent when you look at the raw data and the depot-specific changes from pre-exercise to post-exercise.

The raw changes for each glycogen storage depot within type 1 and type 2 muscle fibers are presented in Figure 1. The researchers also reported an interesting observation related to the orientation of glycogen storage in the most depleted fibers. In the super-depleted type 2 fibers, the researchers found some crystal-like glycogen structures.

These structures were not observed nearly as frequently in type 1 fibers or in fibers with less substantial levels of glycogen depletion.

I try not to be hyperbolic when discussing new research. The implied justification is that glycogen depletion induced by traditional resistance training is negligible in magnitude, because lifters still have plenty of stored glycogen to burn through before full depletion occurs and performance is impacted.

The current findings cast heavy doubts on this line of thinking and its default justification. So, these findings are important, not because they bust a myth that the evidence-based fitness world already abandoned long ago, but because they have potential to shift the high-level, nuanced discussions about dietary carbohydrate moving forward.

Tesch et al 5 studied the glycogen-depleting effect of a pretty rigorous exercise bout including five sets each of front squats, back squats, leg presses, and knee extensions. All sets were taken to failure, with somewhere between reps per set. Participants completed an average of 8.

Finally, Roy and Tarnopolsky 7 assessed muscle glycogen depletion following a full-body workout. While participants completed six upper-body exercises, muscle glycogen was assessed in the vastus lateralis, so the most relevant components of the exercise protocol were three sets of leg extensions, three sets of leg press, and three more sets of leg extension at the end of the workout.

There are two reasons why I love the exercise protocol in the presently reviewed study. The fact that the study was actually conducted in well-trained, competitive lifters is all the better. More importantly in my opinion , this exercise protocol generally replicates the total degree of whole-muscle glycogen depletion observed in the previous glycogen depletion studies I just outlined.

Taken together, this small collection of studies suggests that pretty realistic resistance training protocols are able to induce fairly modest depletion of whole-muscle glycogen content, which is sufficient to markedly reduce the storage of intramyofibrillar glycogen. In fact, as depicted in Figure 1, this exercise bout was able to induce extremely low intramyofibrillar glycogen levels in about half of the type 2 muscle fibers measured.

There is a fairly large hurdle to clear before these findings can actually be applied in practical settings. The presently reviewed study shows that glycogen depletion occurs in a localized, non-uniform manner, with particularly notable depletion occurring in the intramyofibrillar area of type 2 muscle fibers.

But to translate that to practical application, we need to know whether or not that intramyofibrillar depletion actually translates to acute fatigue or impaired contractile function of muscle.

Similar to most beginner and intermediate lifters, athletes, and individuals, the typical fitness enthusiast will have adequate muscle glycogen availability. Assuming there is adequate consumption of calories from a well-balanced diet, most general fitness enthusiasts will have minimal issues with exercise performance due to lack of muscle glycogen availability.

It is important that a strong foundation of nutrition and training behaviors are established for general fitness and overall health improvements. With individuals who are training hard with high volumes, and are highly competitive athletes, muscle glycogen optimization can be a key contributor to sports performance and muscle growth.

For beginners and recreational lifters, however, a well-balanced diet of carbohydrates, fats, and proteins, regardless of meal timing, can suffice if the athlete is consuming enough calories. Below are some general dietary recommendations for beginners and more advanced athletes on how to optimize muscle glycogen if necessary.

As discussed above, muscle glycogen depletion is often not an issue with most beginner, intermediate, and even highly active recreational lifters. Most individuals will be eating enough calories and carbohydrates to adequately refill muscle glycogen stores. In terms of consumption, research suggests consuming 0.

To maximize glycogen and protein synthesis, it is suggested to also ingest around 0. When strength athletes train hard, the muscles use muscle glycogen to fuel contractions that promote the force necessary in movements like deadlifts, squats, presses, cleans, along with other muscle building exercises.

Additionally, urinary nitrogen and other compounds suggesting muscle breakdown levels were significantly lower following carbohydrate supplementation after strenuous exercise, further supporting an increase in muscle growth.

More importantly, however, is that when carbohydrates are paired with a protein and ingested post-workout, research has suggested that the body experiences an increased amount of protein synthesis when compared to a meal containing only carbohydrates 4.

This was also supported by a study that suggested a complete meal consumed post-workout of carbohydrates and a protein source stimulates increased levels of mRNA translation 5. If one experiences periods of time with decreased muscle glycogen levels, then they could experience the following:.

Chronic low levels of muscle glycogen depletion can result in higher levels of muscle fatigue during a session. Often, this can be remedied fairly quickly by ingestion of fast-carbohydrates and closer attention to nutrition, which is discussed below.

With decreased levels of muscle glycogen comes increased levels of muscle fatigue and the inability to promote fast, forceful muscle contractions.

For serious strength athletes, it is important to replenish used muscle glycogen levels after hard training for multiple reasons including, 1. Long story short, without properly addressing low levels of muscle glycogen in hard training, then you can run the risk of depleting energy reserves within muscle tissues and limiting protein synthesis necessary for muscle growth.

Love this article? Take a look below at some of our other sports nutrition articles to improve muscle growth, recovery, and performance. Mike holds a Master's in Exercise Physiology and a Bachelor's in Exercise Science. He's a Certified Strength and Conditioning Specialist CSCS and is the Assistant Strength and Conditioning Coach at New York University.

Mike is also the Founder of J2FIT , a strength and conditioning brand in New York City that offers personal training, online programs, and has an established USAW Olympic Weightlifting club. View All Articles. BarBend is an independent website.

The views expressed on this site may come from individual contributors and do not necessarily reflect the view of BarBend or any other organization. BarBend is the Official Media Partner of USA Weightlifting. Skip to primary navigation Skip to main content Skip to primary sidebar Training Nutrition.

Therefore, in this article we will discuss what you need to know about muscle glycogen, specifically: What is Muscle Glycogen Who Should Be Concerned About Muscle Glycogen?

Dietary Recommendations — Increasing Muscle Glycogen Muscle Glycogen and Serious Athletes Low Levels of Muscle Glycogen and Training What is Muscle Glycogen?

Who Should Be Concerned About Muscle Glycogen? Endurance Athletes Aerobic and anaerobic processes are used to produce energy to fuel endurance athletes. Bodybuilders Assuming beginner and intermediate bodybuilders are consuming adequate amounts of calories; muscle glycogen depletion is often not a high concern.

General Fitness and Health Similar to most beginner and intermediate lifters, athletes, and individuals, the typical fitness enthusiast will have adequate muscle glycogen availability. Beginners and Recreations Lifters As discussed above, muscle glycogen depletion is often not an issue with most beginner, intermediate, and even highly active recreational lifters.

Muscle Glycogen for Serious Athletes When strength athletes train hard, the muscles use muscle glycogen to fuel contractions that promote the force necessary in movements like deadlifts, squats, presses, cleans, along with other muscle building exercises. If one experiences periods of time with decreased muscle glycogen levels, then they could experience the following: Increase Muscle Fatigue Chronic low levels of muscle glycogen depletion can result in higher levels of muscle fatigue during a session.

The Role of Glycogen in Aerobic and Resistance Exercise The role of glycogen stored carbohydrate in muscle in aerobic exercise has been clearly shown to be associated with increased work output and duration Haff et al. Carbohydrate is the body’s preferred substrate during endurance exercise due to its more efficient energy yield per liter of oxygen consumed.

Previous resistance training research suggests that weight training is associated with a consequential depletion of muscle glycogen stores. For instance, Robergs et al.

This article will review two recent articles that further elucidate the role of glycogen in resistance exercise. It is hoped that the personal trainer will gain a better understanding as to the appropriateness of carbohydrate replenishment recommendations for clients engaged in resistance exercise programs.

Energy for Resistance Exercise Due to the intense and short-term nature of individual bouts of resistance training, it would seem likely that this activity would be highly dependent upon muscle glycogen for ATP provision.

In a study by Tesch et al. Biopsies of muscle samples were obtained from the vastus lateralis before and immediately after exercise. This led the authors to conclude that energy sources in addition to muscle glycogen support heavy resistance training.

This suggests that intramuscular lipolysis breakdown of triglycerides may also play a role in energy production during repeated high-intensity exercise. Overall, research suggests that intramuscular glycogen is an important fuel supporting weight training exercise, but not the only substrate.

Subjects 5 young men and one woman performed resistance exercise under a control CON condition no strenuous exercise for at least 48 hours prior to testing and after a carbohydrate restricted program EXP.

The EXP condition included 60 min of submaximal cycling and four 1 minute bouts of maximal exercise, followed by 48 hours of reduced carbohydrate intake. In comparing the CON to the EXP testing condition, the most observable difference was noted in squat performance, with no significant differences in the knee extension trials.

However, there was no difference between the CON and the EXP groups at any of the five contractile speeds of isokinetic knee extensions. In explaining the differing outcomes of the squat sets versus the knee extensions sets to an aerobic and carbohydrate restricted program , the authors summarized previous research that has depicted substrate utilization differences in the type of exercise.

Isometric exercise has been shown to be impaired by reducing glycogen content while no change has been seen in isokinetic exercise. The authors hypothesized the differences in the present study were also due to the type of exercise.

The isokinetic exercise bouts consisted of relatively short duration 1. It was felt the energy production of the isokinetic exercise was predominantly due to the breakdown of creatine phosphate while the utilization of glycogen was much more apparent in the longer lasting squat exercise regime.

The Effect of Carbohydrate Supplementation on Multiple Sessions and Bouts of Resistance Exercise For athletes completing multiple high-intensity strength training sessions per day, maintenance of muscle glycogen stores is critical. In a study by Haff et al. During the second training session, the number of sets and repetitions performed were markedly higher with the carbohydrate consumption, and subjects were able to exercise for 30 minutes longer.

The authors concluded that athletes engaging in multiple exercise sessions per day ranging from mild to high intensity will receive a performance advantage with carbohydrate ingestion via maintenance of intramuscular glycogen stores, due to greater glycogen resynthesis during recovery.

Based on their self-reported 1RMs and years of training experience, it sounds like these participants were pretty solid lifters.

Their relevant demographic data are presented in Table 1. In many of the previous glycogen depletion studies in this area, the researchers look at estimates of whole-muscle glycogen levels via biochemical analysis of tissue homogenate.

They basically take a sample of muscle tissue, grind it up, and see what the glycogen concentration of the ground up muscle tissue is. This precludes them from distinguishing between type 1 and type 2 fibers, let alone distinguishing between distinct glycogen storage depots.

In the presently reviewed study, the researchers used this method to take a quick look at overall glycogen depletion, but they also used a more advanced method with microscopic examination of intact samples of muscle tissue quantitative transmission electron microscopy , which allows them to look at differences between muscle fiber types and specific depots of glycogen storage.

On the manipulation side, the researchers were specifically focused on determining how resistance training impacted glycogen depletion patterns. Participants arrived for testing after an overnight fast and were provided a standardized pre-exercise meal minutes prior to a standardized bout of resistance training.

The exercise session began with some light warmups, followed by three exercises that were intended to target the lower body musculature since glycogen levels were being assessed using vastus lateralis tissue samples. The workout consisted of back squats done in accordance with International Powerlifting Federation standards , deficit deadlifts from a 10cm platform, and dumbbell split squats with the rear foot elevated on a standard bench.

A quick overview of the exact exercises, set and repetition schemes, and approximate loads is presented in Table 2. During their four sets of split squats, participants were instructed to aim for an RPE of about on a point reps in reserve-based RPE scale while completing 12 reps per set.

Participants rested for minutes between sets of squats and deadlifts, and minutes between sets of split squats. In order to assess changes in muscle glycogen, muscle biopsies were obtained about minutes prior to the onset of exercise and immediately minutes after finishing the exercise session.

In terms of outcome variables, the researchers were primarily interested in assessing total muscle glycogen depletion, fiber-specific glycogen depletion, and location-specific depletion of glycogen from the distinct storage depots within muscle tissue intramyofibrillar glycogen, intermyofibrillar glycogen, and subsarcolemmal.

As one would expect, muscle glycogen concentrations decreased and muscle lactate concentrations increased in response to the training bout. Using the more intensive method of glycogen quantification transmission electron microscopy , they were also able to look at distinct, localized glycogen storage depots in type 1 and type 2 muscle fibers.

The relative percentage of total muscle glycogen contained within each localized storage depot intramyofibrillar, intermyofibrillar, and subsarcolemmal is presented below in Table 3. In response to the exercise bout, glycogen stores were depleted in a non-uniform manner. When expressed as a percentage in Table 2, the non-uniformity is hard to see, but it becomes more apparent when you look at the raw data and the depot-specific changes from pre-exercise to post-exercise.

The raw changes for each glycogen storage depot within type 1 and type 2 muscle fibers are presented in Figure 1. The researchers also reported an interesting observation related to the orientation of glycogen storage in the most depleted fibers.

In the super-depleted type 2 fibers, the researchers found some crystal-like glycogen structures. These structures were not observed nearly as frequently in type 1 fibers or in fibers with less substantial levels of glycogen depletion.

I try not to be hyperbolic when discussing new research. The implied justification is that glycogen depletion induced by traditional resistance training is negligible in magnitude, because lifters still have plenty of stored glycogen to burn through before full depletion occurs and performance is impacted.

The current findings cast heavy doubts on this line of thinking and its default justification. So, these findings are important, not because they bust a myth that the evidence-based fitness world already abandoned long ago, but because they have potential to shift the high-level, nuanced discussions about dietary carbohydrate moving forward.

Tesch et al 5 studied the glycogen-depleting effect of a pretty rigorous exercise bout including five sets each of front squats, back squats, leg presses, and knee extensions.

All sets were taken to failure, with somewhere between reps per set. Participants completed an average of 8. Finally, Roy and Tarnopolsky 7 assessed muscle glycogen depletion following a full-body workout.

While participants completed six upper-body exercises, muscle glycogen was assessed in the vastus lateralis, so the most relevant components of the exercise protocol were three sets of leg extensions, three sets of leg press, and three more sets of leg extension at the end of the workout.

There are two reasons why I love the exercise protocol in the presently reviewed study. The fact that the study was actually conducted in well-trained, competitive lifters is all the better.

More importantly in my opinion , this exercise protocol generally replicates the total degree of whole-muscle glycogen depletion observed in the previous glycogen depletion studies I just outlined. Taken together, this small collection of studies suggests that pretty realistic resistance training protocols are able to induce fairly modest depletion of whole-muscle glycogen content, which is sufficient to markedly reduce the storage of intramyofibrillar glycogen.

In fact, as depicted in Figure 1, this exercise bout was able to induce extremely low intramyofibrillar glycogen levels in about half of the type 2 muscle fibers measured.

There is a fairly large hurdle to clear before these findings can actually be applied in practical settings. The presently reviewed study shows that glycogen depletion occurs in a localized, non-uniform manner, with particularly notable depletion occurring in the intramyofibrillar area of type 2 muscle fibers.

But to translate that to practical application, we need to know whether or not that intramyofibrillar depletion actually translates to acute fatigue or impaired contractile function of muscle. As summarized in a recent review paper by Alghannam et al 8 , I think you can make a strong case that we have the evidence to support this translation.

In section 2. Over a series of studies, this research group has demonstrated that reduced intramyofibrillar glycogen levels are associated with impaired calcium release from sarcoplasmic reticula, which appears to increase muscle fatigue and alter muscle contractility 6 , 8.

One of the largest sources of ATP consumption during muscle contraction is the sarcoplasmic reticulum-calcium-ATPase enzyme, and the sodium-potassium-ATPase enzyme is another notable ATP consumer. These enzymes depend on locally available glycogen as a major source of energy, which helps elucidate a mechanistic link between intramyofibrillar glycogen depletion, sarcoplasmic reticulum calcium kinetics, and muscle fatigue 6.

While that evidence has largely come from highly mechanistic studies with limited ecological validity, the same research group has translated their line of research to real-world studies in athletic populations.

In trained triathletes, this group demonstrated that a large reduction in whole-muscle glycogen content induced by prolonged cycling was associated with a significant reduction in sarcoplasmic reticulum calcium release 9.

Four hours after the exercise bout, glycogen levels and calcium release were markedly restored by post-exercise carbohydrate ingestion, but remained suppressed when post-exercise carbohydrate was restricted.

They reported similar findings in trained cross-country skiers 10 , but took the study a step further by specifically assessing localized glycogen depots. However, for the time being, I think these researchers have made a strong case for the idea that intramyofibrillar glycogen is particularly important, and can become depleted to a practically meaningful degree in response to resistance exercise when only modest whole-muscle glycogen depletion is observed.

Back in the s and early s, it seemed like a lot of lifters were pretty fond of micromanaging their carbohydrate timing, and unnecessarily so. These findings do not suggest that the typical lifter needs to return to those old habits of stressing over rapid post-exercise consumption of a carbohydrate source with the perfect molecular weight, glycemic load, monosaccharide composition, and molecular configuration.

Similarly, these findings do not suggest that all lifters need to adopt a super-high-carb diet. As the presently reviewed results suggest, even modest whole-muscle glycogen depletion from traditional resistance exercise can induce a notable reduction of intramyofibrillar glycogen content in type 2 fibers, which could negatively impact performance in the absence of replenishment.

Earlier this year, Dr. Helms and I published a review paper about bodybuilding nutrition guidelines with Dr. Brandon Roberts and Dr.