Glycogen is the form your body uses to store carbohydrate, built from long branched chains of glucose. A typical adult holds roughly 600 g in total, about a pound and a third.1PubMed Central. Fundamentals of glycogen metabolism for coaches and athletes That figure is a moving target, shifting with your size, what you ate, your fitness and your last workout.2PubMed Central. Fundamentals of glycogen metabolism for coaches and athletes Most of it sits in your muscles and can only fuel those muscles, which is why the store shapes how long you can work hard.
Where Your Glycogen Is Stored
Skeletal muscle holds about 500 g, around 80% of the body’s glycogen.3PubMed Central. The Role of Skeletal Muscle Glycogen Breakdown for Regulation of Insulin Sensitivity by Exercise That’s simply because there is so much muscle: it makes up about 40–50% of body weight in healthy young men.4PubMed Central. The Role of Skeletal Muscle Glycogen Breakdown for Regulation of Insulin Sensitivity by Exercise The normal range for muscle glycogen is roughly 300–700 g.5PubMed Central. Fundamentals of glycogen metabolism for coaches and athletes
Muscle glycogen is stored inside each muscle fiber, so the store is spread across every muscle you own rather than kept in one tank. A runner’s leg muscles hold the fuel that powers running, and the arms hold their own separate share. Someone with large leg muscles has more local fuel for cycling and running than a person of the same weight with less muscle.
Fiber type matters a little too. Fast-twitch fibers, used for sprints and lifting, hold somewhat more glycogen than slow-twitch fibers, but the difference is modest, about 16% in human muscle.6PubMed Central. Fibre type‐ and localisation‐specific muscle glycogen utilisation during repeated high‐intensity intermittent exercise Your training mix affects which fibers you lean on, without dramatically changing your total.
The liver holds about 80–100 g.7PubMed Central. The Role of Skeletal Muscle Glycogen Breakdown for Regulation of Insulin Sensitivity by Exercise8PubMed Central. Fundamentals of glycogen metabolism for coaches and athletes It is far more concentrated with glycogen than muscle, but it weighs only about 1.5 kg.9PubMed Central. The Role of Skeletal Muscle Glycogen Breakdown for Regulation of Insulin Sensitivity by Exercise The brain holds glycogen too, in much smaller concentrations than liver or muscle.10PubMed Central. Glycogen in Astrocytes and Neurons: Physiological and Pathological Aspects
The liver’s job is different from muscle’s. Between meals it breaks glycogen down and releases glucose into the blood, which keeps your blood sugar steady when you haven’t eaten for hours. After a carbohydrate meal it does the reverse, pulling glucose out of the blood and linking it into glycogen. Its small store is a shared supply for the whole body, while muscle glycogen stays private to the muscle that holds it. Muscle can’t release glucose into the blood. A hungry brain therefore relies on liver stores, not leg stores, and that is why low blood sugar can hit even when your muscles are full.
How Your Liver Store Rises and Falls Each Day
Liver glycogen changes through the day with how many carbs you eat, the time since your last meal and recent activity.11PubMed Central. Fundamentals of glycogen metabolism for coaches and athletes A fully fed 150 lb runner may hold about 65 g in the liver, with a plausible range of 32–99 g.12runningwritings.com. How Much Glycogen Can the Human Body Store? Overnight that can drop to about 43 g, a 33–40% fall.13runningwritings.com. How Much Glycogen Can the Human Body Store?
What you eat and how much you move shift the number further. A large carbohydrate meal can fill the liver well, while a day of low-carb eating leaves it much lower. Hard exercise draws on the liver to keep blood sugar up, so a long session lowers liver glycogen, not just muscle.
Your body clock also helps time liver glycogen building, which naturally peaks toward the end of your active hours.14PubMed Central. CLOCK Regulates Circadian Rhythms of Hepatic Glycogen Synthesis through Transcriptional Activation of Gys2* A pre-dawn workout or race therefore starts with a partly emptied liver. A carbohydrate breakfast a few hours before a morning event helps top it back up.
On a fasted morning run, your muscle stores are largely intact because you weren’t using them overnight. It is mainly the liver that is lower. That is why a fasted easy run often feels fine, while a hard session can feel flat.
Liver figures are also less certain than muscle figures. They vary widely between people, and estimates for one body size span roughly threefold. Treat any single liver number as a ballpark, not a target.
How Much More You Can Store With Carb Loading
Carb loading means eating a high-carbohydrate diet for a few days before an endurance event, usually with lighter training. The more carbohydrate you eat while loading, the more glycogen your muscles store.15PubMed Central. Dietary Carbohydrate Intake and Skeletal Muscle Glycogen: A Systematic Review and Meta‐Analysis to Determine Optimal Carbohydrate Loading Strategies How much you eat matters most, but training status, how many days you load, and exercise before and during loading also play a role.16PubMed Central. Dietary Carbohydrate Intake and Skeletal Muscle Glycogen: A Systematic Review and Meta‐Analysis to Determine Optimal Carbohydrate Loading Strategies
Even well-loaded muscle appears to hit a ceiling, with no normal loading reaching about 3.9 g of glycogen per 100 g of muscle.17PubMed Central. Glycogen supercompensation in skeletal muscle after cycling or running followed by a high carbohydrate intake the following days: a systematic review and meta-analysis People who start lower gain more, but everyone ends up in a similar top range.18PubMed Central. Glycogen supercompensation in skeletal muscle after cycling or running followed by a high carbohydrate intake the following days: a systematic review and meta-analysis If your muscles begin the week well below that ceiling, a few days of high carbohydrate intake leaves plenty of room to fill. If you already eat lots of carbohydrate and train moderately, you start closer to the top and gain less.
On the plate, a loading day is built around rice, pasta, bread, potatoes and juice. You cut back on fiber and fat to make room for the carbs, and ease training so stores aren’t burned as they fill. This is typically done over the two to three days before a race. Plan by grams of carbohydrate per kilogram of body weight: multiply your weight in kilograms by your chosen daily target, then spread the total across meals and snacks.
Loading matters for efforts beyond roughly 90 minutes. A 5K or a gym session won’t drain normal stores, and everyday eating already fills them for most short workouts.
Women may respond less to modest loading. In one study, men who raised carbs from 55% to 75% of their calories for four days stored 41% more muscle glycogen, while women stored none extra.19PubMed Central. Gender Differences in Carbohydrate Metabolism and Carbohydrate Loading Raising carbs as a share of calories gives women, who often eat fewer total calories, fewer extra grams of carbohydrate.
How Fast Exercise Uses Up Your Glycogen
Exercise intensity is often described as a percentage of your maximum aerobic effort. Above about 75% of that maximum, carbohydrate becomes the main fuel.20Sports Medicine. Muscle Glycogen Metabolism and High-Intensity Exercise Performance: A Narrative Review Working at 64% of maximum used about 2.7 times more glycogen than an easy 31%, and at 84% about 7.4 times more.21PubMed Central. Selective glycogen depletion pattern in human muscle fibres after exercise of varying intensity and at varying pedalling rates
Near and above maximal effort, muscle burns glycogen without enough oxygen, getting much less energy per unit of sugar.22Sports Medicine. Muscle Glycogen Metabolism and High-Intensity Exercise Performance: A Narrative Review Sprints and surges therefore empty stores much faster than steady pacing.
An easy conversational effort uses glycogen slowly because fat supplies a large share of the energy. Pushing the pace even modestly raises glycogen use disproportionately, as the jump from 31% to 64% shows.
Different fibers empty in sequence. Slow-twitch fibers lose glycogen first at moderate efforts, and fast-twitch fibers drain as the work continues.23PubMed Central. Selective glycogen depletion pattern in human muscle fibres after exercise of varying intensity and at varying pedalling rates In three hours of running, muscle glycogen fell about 64%.24PubMed. Metabolic characteristics of keto-adapted ultra-endurance runners Even during intense, prolonged exercise, active muscle doesn’t fall much below about 10% of its starting level.25PubMed Central. Fundamentals of glycogen metabolism for coaches and athletes Women tend to rely less on both liver and muscle glycogen than men at the same relative effort.26PubMed. Menstrual cycle phase and sex influence muscle glycogen utilization and glucose turnover during moderate-intensity endurance exercise Stores rarely empty fully, and fatigue sets in well before zero.
“Hitting the wall” is what happens late in a long race, when low muscle and liver glycogen force a slower pace. It feels like sudden heavy legs and fogginess. Eating carbs during the event slows the drain, and pacing evenly early protects stores for later.
How Fast You Can Refill After Exercise
With less than about 8 hours to recover, neither muscle glycogen nor exercise capacity fully returns.27PubMed Central. Restoration of Muscle Glycogen and Functional Capacity: Role of Post-Exercise Carbohydrate and Protein Co-Ingestion Eating carbohydrate after exercise refills muscle much faster than drinking only water.28PubMed Central. The Effect of Consuming Carbohydrate With and Without Protein on the Rate of Muscle Glycogen Re-synthesis During Short-Term Post-exercise Recovery: a Systematic Review and Meta-analysis Eating carbs at least hourly gives a bigger boost than spacing them out.29PubMed Central. The Effect of Consuming Carbohydrate With and Without Protein on the Rate of Muscle Glycogen Re-synthesis During Short-Term Post-exercise Recovery: a Systematic Review and Meta-analysis
The amount matters. About 1.2 g of carbohydrate per kg of body weight per hour gave a 150% faster refill than 0.8 g.30PubMed Central. Restoration of Muscle Glycogen and Functional Capacity: Role of Post-Exercise Carbohydrate and Protein Co-Ingestion Going higher, to 1.6 g per kg per hour, added nothing more.31PubMed Central. Restoration of Muscle Glycogen and Functional Capacity: Role of Post-Exercise Carbohydrate and Protein Co-Ingestion
To apply this, multiply your weight in kilograms by 1.2 to get grams per hour. Divide that into small portions, such as a banana, a few rice cakes or a sports drink, rather than one huge meal. Keep it up for the first few hours, then return to normal meals.
The first hours are special because muscle is especially ready to take up glucose and store it as glycogen right after a hard session. Hourly eating is aimed at situations where recovery time is short: two sessions in one day, or back-to-back race days. With a full day before the next workout, normal meals do the job, since stores refill anyway.
Protein supports muscle repair. Adding protein isn’t a substitute for the carbohydrate target, but pairing a carb-rich snack with some protein is a sensible default.
The liver refills faster than muscle. In trained cyclists eating a very high 10 g of carbohydrate per kg over 12 hours, liver glycogen refilled quickly but muscle did not fully recover.32PubMed. Carbohydrate intake of 10 g/kg body mass rapidly replenishes liver, but not muscle glycogen contents, during 12 h of post-exercise recovery in well-trained cyclists
Why Glycogen Changes Your Weight
Each gram of muscle glycogen is stored with roughly 3–4 g of water.33PubMed. Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans That’s why body water rises during carb loading.34PubMed. Segmental extracellular and intracellular water distribution and muscle glycogen after 72-h carbohydrate loading using spectroscopic techniques Adding 500 g of glycogen could carry around 1.5–2 kg of water, about 3–4 lb.
This is water bound up with the fuel, not fluid sloshing under the skin, so it isn’t the same as puffiness from salty food. It is released as glycogen is used.
That explains why low-carb weight loss starts so fast. When you cut carbohydrate sharply, the body draws down its glycogen for energy, and the water stored with it leaves the body. The quick drop in the first days is mostly water and stored fuel, not fat. It returns when carbs come back, so judge fat loss over several weeks, not days.
The same logic applies in race week. A heavier feeling after carb loading is normal and reflects stored fuel and water. Don’t cut carbs to offset it.
Does Low-Carb Eating Shrink Your Stores
Keto-adapted ultra-endurance runners burned far more fat than high-carb runners, but their resting muscle glycogen was not significantly different.35PubMed. Metabolic characteristics of keto-adapted ultra-endurance runners Both groups drained about 64% during a three-hour run and refilled to a similar level in two hours.36PubMed. Metabolic characteristics of keto-adapted ultra-endurance runners
That held in long-adapted elite runners, not someone a week into a new diet. Early on, glycogen falls because carbohydrate intake is low and the body hasn’t adjusted, and stores and water drop quickly. Adaptation takes weeks to months. High-intensity efforts still lean on glycogen either way.