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Muscle Glycogen Resynthesis and Athletes

 

Do you want your muscles to feel pumped all the time? Do you want more energy during your workouts? Then fill up your glycogen stores! Glycogen is the storage form of glucose (blood sugar). Muscle glycogen resynthesis or as some say glycogen supercompensation is an important aspect in bodybuilding. Some bodybuilders are so bent on only protein intake that they forget that 2/3 of total glycogen stores are found in skeletal muscle (the other 1/3 being found in the liver). The glycogen found in muscle is generally used for the muscle only and not to maintain blood sugar levels. The glycogen stores in the liver are responsible for maintaining proper blood sugar levels. There are several ways to enhance or improve glycogen stores which will be discussed in a latter part of this article. In this short synopsis of glycogen metabolism as it relates to bodybuilding, I want to explore the details of this interesting topic.

 

2. Biochemistry

Let's start with some basics of glycogen metabolism. If you don't have some knowledge of biochemistry or just simply don't care how it works, please skip to the part about how to increase glycogen stores and current research on this topic. Carbohydrates, specifically glucose, are an important energy source for many human tissues including skeletal muscle. It would not be practical or efficient for your body to store significant amounts of glucose in solution. Therefore, carbohydrate reserves are stored in the form of the branch chained polysaccharide called glycogen. The average bodybuilder sustains about 85 millimoles of glycogen per kilogram of skeletal muscle. A millimole is a simple measurement of the amount of certain compounds in your body. Supercompensation glycogen studies have shown that a trained athlete can achieve at least 175 millimoles. I will discuss how to achieve these glycogen levels in a latter part of this article. When a glycogen-containing muscle cell requires glucose, say during weight training, glucose monomers are removed one at a time from glycogen molecules. This reaction is catalyzed by glycogen phosphorylase. The glucose at this point is released in the form of Glucose-1-phosphate. The first step of glycolysis (the energy producing pathway in muscle cells) is glucose-6-phosphate. Muscle cells contain an enzyme called phosphoglucomutase which can convert glucose 1-phosphate to glucose 6-phosphate at which point it can take part in the steps of glycolysis. Due to the attached phosphate group in this process, none of the glucose resulting from glycogen hydrolysis are able to leave the cell in which they were produced. Liver cells on the other hand, are able to dephosphorylate glucose. Due to this dephosphorylation, the glycogen stores in the liver can release glucose into the blood stream to regulate blood sugar. Glycogen synthesis (the production of glycogen to be stored ) requires the phosphorylation of glucose or the addition of a phosphate group. This allows for activation of the molecule as well as containment within muscle cells. After phosphorylation, glucose reacts with UTP (uridine tri-phosphate) to form UDP glucose. This reaction is effectively irreversible. UDP- glucose monomers are then converted to glycogen by the enzyme glycogen synthase (with the liberation of the UDP). Glycogen synthase activation is considered to be an important regulatory step in glycogen synthesis (1). Glycogenin, a glycoprotein, serves as a guide for all glycogen synthesis. It has a function of priming glycogen synthesis as well as activating glycogen synthase. I will discuss this interesting compound further a little later. Muscle glycogen reserves are mobilized in situations of stress. Phosphorylase kinase is an enzyme which catalyses glycogen phosphorylase. The activity of glycogen phosphorylase is increased by epinephrine (adrenaline). Muscle contraction is initiated by a rise in Ca+2 ion concentration. Ca+2 ions also increase the activity of phosphorylase kinase. Proper calcium intake is essential for muscle contraction . I would recommend at least 1600mg of calcium daily for bodybuilders. A secondary beneficial effect of calcium is that it has been shown to lower blood pressure. Magnesium and potassium supplementation may also be necessary for proper electrolyte balance if taking a calcium supplement.

When glucose is ingested and goes into the blood stream from the digestive tract, it stimulates the release of the peptide hormone insulin from the pancreas. Insulin binds to specific receptors in cell membranes and facilitates diffusion of glucose into the cell. Normally the cell membranes are impermeable to glucose , but when a cell receptor is activated the membrane allows for a rapid entry of glucose into the cells. Insulin also helps activate glycogen synthase (2) and allows cell membranes to become more permeable to certain amino acids, creatine, and some minerals. Insulin causes glucose transport proteins (GLUT) to increase their activity allowing for increased glucose uptake by muscle cells. Two of these transporters have been found in skeletal muscle: GLUT 1, which is present in low levels, and GLUT 4, which is the major isoform in muscle and is responsible for the increase in glucose transport in response to insulin and muscle contractions (2, 3, 4, 5) A rapid transport of glucose into the cell requires the presence of GLUT 4 transporters on the cell surface, and translocation of these from the Golgi apparatus requires insulin. It is believed that both insulin and exercise stimulate the translocation of GLUT 4 transporters from an intracellular pool to the plasma membrane of skeletal muscle (6). According to some research, there may be two separate intracellular pools of glucose transporters, one accessible for translocation by the actions of insulin and one accessible by the effect of exercise (7). Both exercise (muscle contraction to be specific) and insulin stimulate an increase in glucose uptake by muscle. It has also been established that glycogen can be resynthesized from lactate in skeletal muscle (8). There is ample evidence which suggests that exercise during recovery impede glycogen synthesis. This is why I recommend that you refrain from any cardiovascular work right after resistance training. It may inhibit glycogen resynthesis and not let you recover from your weight training session. The best time for cardiovascular work is early in the morning on an empty stomach. This may allow for the most fat loss.

There have only been two comprehensive studies (9,10) that have investigated muscle glycogen synthesis after resistance exercise. Pascoe et al (9) reported a 31% decrease in muscle glycogen levels after resistance training. Robergs et al (10) reported muscle glycogen degradations of about 38% after resistance training. Muscle glycogen resynthesis after resistance exercise (weight lifting) is considerably faster than prolonged aerobic exercise (8). Eccentric exercise has been associated with ultrastructural muscle damage, leakage of intracellular enzymes, delayed onset muscle soreness , AND reduced rates of glycogen resynthesis (11,12). Some evidence suggests that the anti-inflammatory cells which enter muscle tissue in response to the eccentrically induced damage compete with the muscle cells for available plasma glucose (12). In addition, these inflammatory cells may produce a metabolic factor that shifts muscle metabolism towards glycogenolysis (glycogen breakdown) and away from glycogen synthesis. It is speculated that the damage resulting form eccentric exercise interfered with the insertion of the GLUT 4 protein into the plasma membrane and increased the rate of degradation or the rate of production of this glucose transporter protein (12). The evidence sited above shows that eccentric contractions and subsequent muscle damage impair muscle glycogen resynthesis. I would recommend more explosive, concentric type of movements to enhance glycogen resynthesis after resistance training. This would especially be necessary while carbohydrate loading/depleting (before a bodybuilding competition for example). The recruitment of more fast twitch glycolytic muscle fibers may also enhance glycogen synthesis (8).

 

Exercise stimulates muscle glucose uptake both directly and by increasing the sensitivity of this process to insulin. Increased fat intake and intracellular triglycerides may cause insulin resistance and hamper muscle glycogen resynthesis. According to one study, exercise increased insulin sensitivity in normal subjects because of a two fold increase in insulin-stimulated glycogen synthesis in muscle, due to an increase in insulin-stimulated glucose transport-phosphorylation (13). Since insulin sensitivity is highest after resistance exercise, it is vital to take a high glycemic index drink immediately after training. This stimulates the secretion of insulin to allow rapid muscle glycogen resynthesis. The general formula is to consume about 1.5 grams of high glycemic index carbohydrates per kilogram of bodyweight after weight training. Glycogen restoration rate is higher following glucose feeding as compared with fructose feeding because of glucose's higher glycemic index rating. Some people have mentioned to me that protein is also needed along with carbohydrates to increase muscle glycogen resynthesis. I believe if you consume a high glycemic index carbohydrate after training at the amount given above, then additional protein will not improve muscle glycogen resynthesis (14). If you are on a ketogenic type of a diet than consuming certain amino acids (namely branched chain) may allow for an insulin response causing an increase in muscle glycogen resynthesis. By the way, supercompensated muscle glycogen levels can maintained at least three days after carb loading on a moderate carbohydrate diet according to a study at the Naval Health Research Center in San Diego.

Glycogenin, which I mentioned previously, primes glycogen synthesis. The amount of glycogenin will influence how much glycogen a cell can store (15). Thus the production of active glycogenin primer in the cell has the potential to be the overall rate limiting process in glycogen formation. A company called Upstate Biotechnology markets glycogenin but not for human consumption. I don't believe that the FDA has approved synthetic glycogenin for human consumption. Another component of glycogen metabolism has been discovered which may even have greater influence on total glycogen stores than does glycogenin. This is the low molecular mass form of glycogen called proglycogen (15). If proglycogen could be converted into macroglycogen , muscle glycogen levels may increase significantly. I believe that this will be the next big step in glycogen resynthesis advancements.

 

3. Increasing muscle glycogen levels

Now on to the most critical part of muscle glycogen resynthesis. How do you increase muscle glycogen levels? There are several supplements and techniques to allow for increased glycogen storage. One way is taking a glutamine supplement. Glutamine causes a significant increase in muscle glycogen deposition through an unknown mechanism. According to one university study, a physiological concentration of glutamine stimulates glycogen synthesis from glucose and gluconeogenic pre-cursors (16). So glutamine along with your post workout high glycemic index carbohydrates may increase glutamine and glycogen in the muscle. I would recommend at least 5-10 grams of glutamine at this time to allow for glycogen recompensation. In another research study on humans, an intravenous drip of glutamine, raising blood levels about 70% above normal, increased muscle glycogen (17). Some top quality glutamine supplements I would recommend are Cytovol by EAS and SuperGlu by GURUetc. There is also a doctor named Elias Meezan who is in the process of patenting artificial primers for glycogen synthesis. Properties of these compounds enable them to readily penetrate cells chemically intact so that they have access to glycogenin and glycogen synthase. The unique structural and metabolic properties of these compounds make it highly likely that in addition to priming glycogen synthesis on their own, they could act synergistically with other drugs to stimulate glucose disposal and glycogen synthesis. This is real exciting news for bodybuilders and diabetics as well. Next, there are those glucose disposing agents or so called "insulin mimickers" such as vanadyl sulfate, chromium picolinate, metformin, and phenformin. Alpha lipoic acid also shows potential as a glucose disposing agent. In Germany, it is used as a treatment for peripheral neuropathy, a common complication of diabetes. It speeds the removal of glucose from the blood stream, at least partly by enhancing insulin function and reducing insulin resistance. The richest food source of alpha lipoic acid is red meat. Vanadyl sulfate helps to trigger glucose transporters much like insulin, obviously meaning increased glycogen stores and better assimilation of protein by muscle tissue. Higher glycogen stores mean better "pumps" in the gym and more energy during workouts. Chromium picolinate helps insulin function by regulating glucose tolerance factor which helps insulin bind to muscle cells. This may especially be important to insulin resistant bodybuilders. Metformin, which is sold as Glucophage in America, is an extremely powerful glucose disposing agent used to manage diabetes. Phenformin is similar but causes the negative side effect of lactic acidosis. Metformin is a prescription item. Phenformin can be found in Mexico where it is sold under the brand name of Debeone. Doing explosive concentric movements and limiting eccentric type of training (i.e. long negatives) may also increase glycogen stores. Carbohydrate depleting and then reloading (glycogen supercompensation) may allow you to increase glycogen stores two fold, as mentioned above.

 

So basically to allow for the most glycogen stores I would definitely recommend a vanadyl or chromium supplement. V2G by EAS and Vanadyl ph by Sportpharma seem to be two effective vanadyl supplements. Training intensely, depleting glycogen stores, may also allow for rapid glycogen resynthesis. There is a great advantage to carb loading before a bodybuilding competition. The method I recommend is this: 7 days out from a show, start carb depleting by consuming 1 gram of carbohydrates per kilogram of bodyweight. This depleting phase will increase glycogen synthase activity and prime your body for glycogen supercompensation. Training during this time should consist of heavy, explosive (concentric) movements for low repetitions. Glucagon levels will start rising at this point to help maintain blood sugar levels. After three days of depleting, start carb loading by consuming 3 grams per kilogram of bodyweight daily along with a glutamine and glucose disposing supplement for three days. Consume a greater amount of those carbs earlier in the day and taper down as the day progresses. Make sure to consume plenty of complex carbohydrates during the loading phase such as sweet potatoes ,vegetables, brown rice, and multi-grain oatmeal. The loading phase should allow for glycogen supercompensation and fill your glycogen stores to the gills causing enlarged muscles and harder definition. You should try carb loading/depleting about 3 weeks before the show to make sure it works perfectly. The slightest mistake can cause water retention and a smooth appearance to muscles. This formula has worked for me in many competitions over the years.

 

In conclusion, glycogen resynthesis plays an important role in bodybuilding and proper carbohydrate depleting/loading can make the difference between winning a bodybuilding competition or looking like a balloon and losing. Advances in glycogen synthesis are currently being made and the future looks bright for bodybuilders.

 

References

  1. Ivy JL (1991). Muscle glycogen synthesis before and after exercise. Sports Med 11(1), 6-19

  2. Newsholme EA, Leech AR. (1984). Biochemistry for the medical sciences. New York: John Wiley & Sons, 38-42; 312-30; 444-454

  3. Friedman JE, Neufer PD, Dohm GL. (1991). Regulation of glycogen resynthesis following exercise. Dietary considerations. Sports Med 11(4), 232-243.

  4. Rodnick KJ, Henriksen EJ, James DE, et al. (1992). Exercise training, glucose transporters, and glucose transport in rat skeletal muscles. Am. J. Physiol. 262(1), C9-C14

  5. Klip A, Ramal T, Young DA, et al. (1987). Insulin-induced translocation of glucose transporters in rat hindlimb muscles. FEBS Lett. 224(1), 224-230

  6. Wallberg-Henriksson H, Constable SH, Young DA, et al. (1988). Glucose transport into rat skeletal muscle: interaction between exercise and insulin. J. Appl. Physiol. 65(2), 909-913

  7. Gao J,Ren J, Gulve EA, et al. (1994). Additive effect of contractions and insulin on GLUT-4 translocation into the sarcolemma. J Appl Physiol 77(4), 1597-1601

  8. Pascoe DD, Gladden LB. (1996). Muscle glycogen resynthesis after short term, high intensity exercise and resistance exercise. Sports Med 21(2), 98-118

  9. Pascoe DD, Costill DL, Fink WJ, et al. (1993). Glycogen resynthesis in skeletal muscle following resistive exercise. Med Sci Sports Exerc 25(3), 349-354

  10. Robergs RA, Pearson DR, Costill DL, et al. (1991). Muscle glycogenolysis during differing intensities of weight-resistance exercise. J Appl Physiol 70(4), 1700-1706

  11. O'Reily KP, Warhol MJ, Fielding RA, et al . (1987). Eccentric exercise-induced muscle damage impairs muscle glycogen repletion. J. Appl. Physiol. 63(1), 252-256

  12. Costill DL, Pascoe DD, Fink WJ, et al. (1990). Impaired muscle glycogen resynthesis after eccentric exercise. J Appl Physiol 69(1), 46-50

  13. Perseghin G, Price TB, Petersen KF, Roden M, Cline GW, Gerow K, Rothman DL, Shulman GI (1996). Increased glucose transport-phosphorylation and muscle glycogen synthesis after exercise training in insulin-resistant subjects. N. Engl. J. Med. 335(18), 1357-1362

  14. Zawadski KM, Yaspelkis BB, Ivy JL. (1992). Carbohydrate-protein complex increases the rate of muscle glycogen storage after exercise. J Appl Physiol 72(5), 1854-1859

  15. Alonso MD, Lomako J, Lomako WM, Whelan WJ, et al. (1995). A new look at the biogenesis of glycogen. FASEB J. 9(12), 1126-1137

  16. Lavoinne A, Baquet A, Hue L (1987). Stimulation of glycogen synthesis and lipogenesis by glutamine in isolated rat hepatocytes. Biochem. J. 248(2), 429-437

  17. Varnier M, Leese GP, Thompson J, Rennie MJ, et al. (1995). Stimulatory effect of glutamine on glycogen accumulation in human skeletal muscle. Am. J. Physiol. 269(2), E309-E315

 

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