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. If your training and racing goes beyond low-level aerobic exercise, you will need to use glycogen to perform at your peak potential. 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. 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. 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. Train with adequate glycogen stores by eating carbohydrates in your daily diet. Just prioritize a balanced diet rich in healthy carbohydrates like whole grains, along with plenty of good fat and rich protein. Finally, building a strong endurance base will help you be a better fat burner at higher intensities.
Since even the leanest riders have abundant fat stores that means you can ride longer and harder before you burn through your limited glycogen supply. There are some cyclists who experiment with carbohydrate manipulation. Of course, all diets are a personal choice, but we find the best diets are the ones you can adhere to over the long haul that support your training. Sticking to a well-balanced diet that fuels your workouts, regulates your mood, and helps you sleep well instead of obsessing over carb-counting is far better for recreational, competitive, and research is showing maybe even most pro athletes.
That way, you can take all that energy you would spend tracking food and channel it into quality training instead. Bikes and Gear. United States. Type keyword s to search. However, it appears that many athletes may not be consuming enough carbohydrates on a daily basis to fully restore muscle glycogen. For example, Mullins et al. The results were similar for professional English soccer players who ingested an average of 4. The synthesis of muscle glycogen depends upon uptake of glucose molecules from the blood into muscle cells.
When carbohydrates are ingested at rest—and in the recovery period after exercise—the entry of glucose into muscle cells is facilitated by the hormone insulin. When glucose enters the muscle cell at rest or during exercise, it is immediately phosphorylated to glucosephosphate by the enzyme hexokinase. Glucosephosphate can then be oxidized through glycolysis and the Krebs cycle to produce ATP for immediate use by the cell, or it can be stored as glycogen.
In fact, glucosephosphate allosterically activates glycogen synthase, stimulating the addition of glucose molecules to the glycogen particle. The activity of the glycogen synthase enzyme is controlled by a cascade of events that rely on phosphorylation and dephosphorylation reactions that decrease and increase the activity of the enzyme in concert with similar phosphorylation-dephosphorylation reactions that control muscle glycogenolysis via the glycogen phosphorylation enzyme described below see Figure 3.
A simplified overview of glycogen metabolism at rest and during exercise. The sarcolemma separates the muscle cell interior from the interstitial fluid that surrounds the cell. At rest left side , the consumption of carbohydrate stimulates the release of insulin from the pancreas. Insulin molecules bind to insulin receptors embedded in the sarcolemma. That binding sparks a cascade of intracellular responses that result in the movement of GLUT4 glucose transporters from the interior of the muscle cell into the sarcolemma, allowing for glucose to move into the cell.
Once inside the muscle cell, glucose molecules are readied for inclusion into glycogen. Glycogenin is an enzyme that forms the center of glycogen particles, allowing for the initial formation of glycogen strands. During exercise right side , GLUT4 transporters move into the sarcolemma without the assistance of insulin, aiding in glucose uptake into the cell. Simultaneously, glycogen degradation increases in response to changes in the concentration of metabolites inside the cell.
The glucose molecules from the blood and those released from glycogen are oxidized to produce the adenosine triphosphate ATP molecules required to sustain muscle contraction. The activity of glycogen synthase is also influenced by the glycogen content of the muscle cell; high glycogen synthase activity is associated with low glycogen levels.
After exercise, the restoration of muscle glycogen occurs in a biphasic manner. Periodic carbohydrate supplementation can result in supercompensation of glycogen stores, an advantage after tasks requiring hours of sustained physical effort. In fact, the second-phase effect can be sustained for several days when carbohydrate intake is maintained.
During vigorous exercise, insulin release is blunted, and epinephrine adrenalin is released from the adrenal glands. Epinephrine causes phosphorylation of intramyofibrillar glycogen synthase, ensuring that glycogen synthesis is slowed as glycogen degradation rapidly increases.
As exercise progresses, the activity of glycogen phosphorylase falls as glycogen stores are reduced and as plasma free fatty acids become more available as substrates. Endurance training increases muscle glycogen stores and reduces the reliance on glycogen as a result of the increased use of free fatty acids by active muscle cells, 40 a metabolic adaptation that allows for improved performance. Conversely, the depletion of muscle glycogen causes fatigue.
For example, Krustrup et al. If daily carbohydrate intake is insufficient to fully replace the glycogen metabolized during hard labor or training, muscle glycogen concentration in active muscles will fall progressively over a period of days, a circumstance that is well established in the scientific literature.
As a result, they accidentally benefit from the enhanced metabolic signaling associated with low muscle glycogen. There is even less certainty regarding how muscle glycogen stores influence the adaptations associated with resistance training because there are far fewer studies compared to the number of studies that have focused on the influence of glycogen levels on the adaptations to endurance and interval training.
It may be that the average value for muscle glycogen concentration does not accurately reflect the intramyofibrillar glycogen stores, which appear to have the greatest impact on muscle function. Figure 4 depicts how muscle glycogen levels might vary during 4 days of hard training followed by 2 days of light training. Muscle glycogen levels can vary widely during training, only reaching supercompensated levels after a few days of rest and light training.
In this example, muscle glycogen levels decline during training sessions and are partially restored during subsequent rest and after adequate carbohydrate intake. During hard 2-a-day training sessions day 3 , glycogen concentration can be lowered to the point at which contractile dysfunction fatigue occurs. Illustration based on data from Sherman and Wimer Whenever muscle glycogen stores are reduced as a result of physical activity, consumption of an adequate amount of carbohydrate is required to restore glycogen to normal levels or above supercompensation.
Athletes who train hard most days of the week, at times completing multiple training sessions each day, likely do so with muscle glycogen stores that are rarely fully replenished.
For example, Sherman et al. In their review of the literature, Sherman and Wimer 85 came to the conclusion that high-carbohydrate diets can prevent a fall in muscle glycogen stores over weeks of intense training; in contrast, moderate-carbohydrate diets maintain muscle glycogen stores at levels that are lower but still sufficient to meet the demands of hard training.
In an exhaustive review of the literature on dietary carbohydrate intake among athletes, Burke et al. Although training capacity and performance may not be adversely affected by the consumption of moderate-carbohydrate diets, performance is impaired on low-carbohydrate diets. Burke et al. The high-carbohydrate group improved their performance by 6. In practical terms, athletes should be educated and encouraged to consume enough carbohydrates to replenish at least a sizable portion of their muscle glycogen stores so that training intensity can be maintained from day to day.
Fortunately, athletes in training tend to gravitate to high-carbohydrate diets, 1 helping ensure that glycogen stores do not drop so low that training is impaired. Immediately after physical activity, muscle cells that sustained a substantial decrease in glycogen content are metabolically prepared for rapid glycogenesis.
In brief, glycogen use during exercise turns on glycogen synthesis during recovery. When carbohydrates are ingested soon after exercise, insulin release from the pancreas, insulin sensitivity in muscle cells, glucose uptake by muscle cells, and glycogen synthase activity within muscle cells all increase, 94 responses that can remain elevated for 48 hours. As noted above, timing of carbohydrate intake following physical activity is very important during training and competition requiring multiple efforts during a single day.
Daily carbohydrate intake should reflect the extent of carbohydrate oxidation during training: low on light training days, substantially higher on days of intense or prolonged training.
Table 3 contains related practical recommendations. Recommendations for daily carbohydrate intake for athletes involved in repeated days of strenuous, prolonged physical activity and training. Adapted from Thomas et al. In their review of the literature, Burke et al. It is true that fructose better stimulates liver glycogen restoration and glucose does the same for muscle glycogen, but most physically active people normally ingest enough fructose and glucose in foods and beverages to restore liver glycogen.
Consequently, there is no need to be concerned with the adequacy of dietary fructose intake. It should be noted that combinations of glucose, fructose, and sucrose consumed in sports drinks during exercise have been shown to enhance the rate of fluid absorption from the proximal small intestine and improve the rate of carbohydrate oxidation during exercise, , 2 important factors in sustaining exercise performance.
Solid and liquid forms of carbohydrates are associated with similar rates of glycogen synthesis, — so athletes can meet their daily carbohydrate needs by consuming the carbohydrate-rich foods and beverages they most enjoy.
Interestingly, Cramer et al. In the hours soon after exercise, consuming high—glycemic index GI foods can speed muscle glycogen restoration. Low-GI foods are digested and absorbed more slowly than high-GI foods, differences that result in a slower rise in blood glucose and insulin levels, an effect that can last for hours after eating.
The meals were consumed 2 hours prior to exercise. Compared with a placebo treatment no meal , both the low- and high-GI meals improved the total run distance during sprints conducted in the last 15 minutes of the minute session.
In contrast with no pre-exercise meal, muscle glycogen levels prior to the final minute segment of exercise were similarly higher with both low- and high-GI meals.
The authors attributed improved run performance to higher muscle and possibly liver glycogen levels prior to the final sprints. Consuming high-GI carbohydrates is effective in increasing muscle glycogen stores after exercise. Increasing the carbohydrate content of the diet to However, Brown et al. As is often the case in science, additional research is needed to further clarify the conditions in which consuming high-GI foods benefits glycogen restoration and performance.
Waxy starches from varietals of potatoes, corn maize , and barley are high in amylopectin and low in amylose; amylopectin is less resistant to digestion because its glucose chains are more highly branched compared with amylose. For that reason, waxy starches have been studied to assess how their ingestion influences glycogen metabolism and exercise performance.
Postexercise muscle glycogen concentrations were similar among treatments, but 24 hours later, less glycogen had been replenished with resistant starch compared with the other treatments. Total glycogen repletion with glucose was greater than that with waxy starch was greater than that with maltodextrin was greater than that with resistant starch.
A companion study by Goodpastor et al. Additional research on the metabolic and performance responses to the ingestion of waxy starches is warranted simply because of the dearth of research in this area. In terms of overall health, high-quality carbohydrates from unprocessed or minimally processed whole grains, vegetables, beans, dairy foods, and fruits also provide numerous vitamins, minerals, fiber, and many important phytonutrients. Increased consumption of high-quality carbohydrate foods, such as potatoes and grains, can help ensure adequate consumption of nutrients vital to health, recovery, repair, adaptation, growth, and performance.
Aside from the purposeful manipulation of muscle glycogen concentration by diet and training nutrition periodization , periods of extended fasting during Ramadan or in attempts to lose body weight result in metabolic responses that are usually contrary to maintaining high muscle glycogen concentrations, especially if training continues during the fasted state.
Prolonged fasting and very low—carbohydrate diets result in ketosis ketoacidosis , sparing liver and muscle glycogen. As a result, ketotic diets and the ingestion of ketone bodies have been suggested as possible ergogenic aids, particularly for endurance and ultra-endurance athletes. Related to that conclusion, Vandoorne et al. In short, more research is needed to further clarify the metabolic and performance responses to ketosis—whether induced by fasting, prolonged low-carbohydrate diets, or by the ingestion of ketone bodies—across performance parameters, with special reference to the mental and physical responses during ultra-endurance events when fat oxidation normally predominates.
This relatively slow time course makes it impossible for those engaged in multiple bouts of intense exercise during a single day to fully restore muscle glycogen between training sessions or competitive efforts. However, it is possible to maximize the rate of short-term muscle glycogen repletion so that athletes can replenish more muscle glycogen than might otherwise be possible. Consuming proteins with carbohydrates may be beneficial in stimulating rapid glycogenesis in the hours immediately following exercise, 65 a finding that has implications for speeding recovery between demanding bouts of exercise within the same day.
A greater glycogen storage rate may be due to increased muscle glucose uptake and enhanced signaling pathways made possible by the influx of amino acids. Protein consumption also induces a rise in blood insulin concentration that augments the insulinemic response to carbohydrate ingestion, increasing the rate of glycogen repletion. Consumption of 0.
It is clear that adequate consumption of proteins stimulates muscle protein synthesis during rest, although consuming proteins during exercise does not appear to benefit performance or immune function or reduce muscle damage. Multiday supplementation with creatine monohydrate along with an adequate amount of carbohydrates has been reported to increase muscle glycogen synthesis compared with carbohydrate ingestion alone.
Males and females appear to restore muscle glycogen at similar rates following exercise, as long as sufficient carbohydrates and energy are consumed. The additional protein intake might also help facilitate glycogen synthesis, especially when carbohydrate intake is low. The Dietary Guidelines for Americans identifies gap nutrients as dietary fiber, choline, potassium, magnesium, calcium, and vitamins A, D, E, and C.
That might take 2 to 4 hours, depending on the total muscle mass, intensity and type of exercise. This liver glycogen feeds into the bloodstream blood glucose and fuels your brain.
Depleted liver glycogen stores lead to low blood sugar and feeling light-headed. The average pound athlete has only 1, to 2, calories of stored carbohydrates glycogen , but over 80, to , calories of stored fat. What happens overnight? As you exercise, your body breaks down glycogen into glucose for energy.
Once glycogen stores are depleted, your body runs out of fuel and you will begin to feel tired. Consuming carbohydrates while you exercise will prevent glycogen depletion. To start burning fat, you need to diminish your glycogen stores so your body has no other choice than to use stored fat for energy.
Excess glucose gets stored in the liver as glycogen or, with the help of insulin, converted into fatty acids, circulated to other parts of the body and stored as fat in adipose tissue. When there is an overabundance of fatty acids, fat also builds up in the liver. A hour fasting period reduced the liver glycogen to a very low level, which was depressed only slightly more by the fatiguing exercise. It reduced the muscle glycogen by one-third; after 24 hours the rate of fall was much slower.
Fat burning typically begins after approximately 12 hours of fasting and escalates between 16 and 24 hours of fasting. Exercise helps a person deplete the glycogen stores in their body. In most cases, the glycogen stores become replenished when a person eats carbs. If a person is on a low-carb diet, they will not be replenishing their glycogen stores.
It can take some time for the body to learn to use fat stores instead of glycogen. Those first 1, calories are stored in your liver and muscle immediately. These are called glycogen calories. This all starts happening after 4 hours.
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