Presentation on theme: "Carbohydrates in Exercise and Recovery"— Presentation transcript:
1 Carbohydrates in Exercise and Recovery Advanced Level
2 Module I Carbohydrates: Definitions, Digestion, and Absorption Review of Carbohydrate MetabolismCarbohydrates: Glycogen Storage
3 Carbohydrates: Definitions, Digestion, and Absorption
4 Importance of Carbohydrates in Sports Nutrition Carbohydrates are a major fuel source for exercising muscle, especially as exercise intensity and duration increaseTypes of carbohydrate oxidationExogenous: Oxidizing carbohydrates ingested from the dietEndogenous: Breaking down stored carbohydrate (ie, glycogen) for energy needsCarbohydrates can also influence fluid absorption from the intestine (hydration)Some carbohydrates can cause gastrointestinal intolerance and could impair performance for that reasonUnited States Anti-doping Agency. Optimal dietary intake guide. Available at: Accessed January 31, 2011.
5 Carbohydrate Digestion and Absorption Carbohydrates are found in the diet asFree monosaccharide (1 sugar unit) orLarger saccharides (chains of monosaccharides)Enzymes must digest larger saccharides down to individual monosaccharides before these monosaccharides can be absorbedCarbohydrates that escape absorption make their way to the colon (variable degrees of bacterial fermentation)Monosaccharides are absorbed from the intestine mainly via active transport (energy-requiring) or facilitated diffusionBoth active transport and facilitated diffusion require transportersSGLT (Active transport)GLUT (Facilitated diffusion)Abbreviations: SGLT, sodium-glucose linked transporter; GLUT, glucose transporter.Holmes R. J Clin Pathol. 1971;S3-5: doi: /jcp.s
6 Why Do We Need to Know About Carbohydrate Absorption in Sports Nutrition? The ability of the intestine to absorb a carbohydrate can be the rate-limiting step for its delivery to muscle cells for fuel useIntestinal sugar transporters can become saturated, resulting in malabsorption of a carbohydrateConcept of multiple transportable carbohydratesUse a blend of sugars that require different transporter systemsMay increase carbohydrate absorption relative to using just a single sugarEnzyme systems in the intestine may be insufficient to digest some carbohydrates (eg, lactose intolerance)
7 Sugar Transport in an Intestinal Epithelial Cell Intestinal LumenEnterocyteBloodGlucoseGalactoseFructoseGlucoseGalactoseFructoseGlucoseGalactoseGlucoseGalactoseSGLT1GLUT22 Na+2 Na+Na+Na+ATPFructoseFructoseADP + PiGLUT5K+K+Apical membraneBasolateral membraneAbbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; GLUT, glucose transporter; K, potassium; Na, sodium; Pi, phosphate group; SGLT, sodium-glucose linked transporter. Scheepers A, et al. JPEN J of Parenter Enteral Nutr. 2004;28(5): Drozdowski LA, et al. World J Gastroenterol. 2006;12(11):
8 Major Dietary Monosaccharides No Digestion Required for Absorption Glucose; from corn and other plantsAlso called dextroseAbsorbed primarily by active transport (SGLT1), with facilitated diffusion (GLUT2) used to a lesser extent when intraluminal glucose concentrations are highSGLT1 requires sodium co-transport and ATPTransported out of enterocyte via GLUT2Muscles express GLUT4 transporters to take up glucose from the bloodFructose; fruit sugarAbsorbed by facilitated diffusion (primarily GLUT5)Simultaneous presence of glucose stimulates fructose uptake, probably by GLUT2Fructose is taken up almost entirely by the liver; very little circulates in the bloodGalactoseIs a component of lactose (milk sugar)Is transported from the intestine similarly to glucoseConverted to glucose in the liverAbbreviations: ATP, adenosine triphosphate; SGLT, sodium-glucose linked transporter; GLUT, glucose transporter. McGrane MM. Carbohydrate metabolism—synthesis and oxidation. In: Stipanuk M. Biochemical, Physiological & Molecular Aspects of Human Nutrition. 2nd Edition. Saunders/Elsevier; 2006: chap 12.
9 Common Dietary Disaccharides Sucrose (table sugar)Extracted from sugar cane and beetsComposed of glucose and fructose (alpha-1,2 linked)Digested by sucrase-isomaltase complexAnchored in brush border of small intestineLactosePrimary sugar in virtually all mammalian milksComposed of glucose and galactose (beta-1,4 linked)Digested by brush border lactase-phlorizin hydrolaseHertzler SR, et al. Intestinal disaccharidase depletions. In: Shils ME, et al. Modern Nutrition in Health and Disease. 10th Edition. Baltimore, MD: Lippincott Williams & Wilkins; 2006: pp
10 Common Dietary Disaccharides (continued) MaltoseFound in some fermented beverages (eg, beer) and is also an intermediate product in starch digestionComposed of 2 glucose molecules (alpha-1,4 linked)Digested by maltase-glucoamylaseTrehaloseFound in mushroomsComposed of 2 glucose molecules (alpha-1,1 linked)Digested by trehalaseHertzler SR, et al. Intestinal disaccharidase depletions. In: Shils ME, et al. Modern Nutrition in Health and Disease. 10th Edition. Baltimore, MD: Lippincott Williams & Wilkins; 2006: pp
11 Oligosaccharides (3-10 Monosaccharide Units) Oligosaccharides are found in human milk and in a variety of fruits and vegetablesMany of these are not digestible by human enzymesExamplesStachyose (galactose-glucose-fructose)Raffinose (galactose-galactose-glucose-fructose)Fructooligosaccharides and oligofructoseChains of fructose units sometimes terminated with glucoseGlucose polymers/maltodextrinsMost are rapidly digestible; some are resistant to digestionCarbohydrates. In: Gropper SS, et al. Advanced Nutrition and Human Metabolism. 4th Edition. Belmont, CA: Wadsworth, Cengage Learning.; 2005: pp
12 Digestible Polysaccharides Plant starches (digestion via salivary and pancreatic amylases)AmylopectinChains of alpha-1,4 linked glucose with alpha-1,6 branch points (renders the starch more digestible)AmyloseStraight chains of glucose linked by alpha-1,4 bondsLess digestible than amylopectinAnimal starchGlycogenStorage form of glucose in liver and musclesSimilar in structure to amylopectin, but more highly branchedCarbohydrates. In: Gropper SS, et al. Advanced Nutrition and Human Metabolism. 4th Edition. Belmont, CA: Wadsworth, Cengage Learning.; 2005: pp
13 Nondigestible Polysaccharides (Dietary Fibers) CelluloseChain of glucose units linked by beta-1,4 bondsHemicellulosesPectinsGumsMucilagesSome indigestible oligosaccharides would count as dietary fibersCarbohydrates. In: Gropper SS, et al. Advanced Nutrition and Human Metabolism. 4th Edition. Belmont, CA: Wadsworth, Cengage Learning.; 2005: pp
14 What Is High-Fructose Corn Syrup? Cornstarch converted to a syrup that is essentially 100% dextrose (glucose)Enzymes isomerize dextrose to produce 42% fructose syrup (HFCS-42)Refiners draw HFCS-42 through an ion exchange column that retains fructoseResult is HFCS-90 syrupThe HFCS-90 syrup is blended with HFCS-42Result is HFCS-55The HFCS-55 syrup is the type used mainly in beverage industrySyrup is 55% fructose, 45% dextroseEssentially no different than sucrose (table sugar; 50% fructose, 50% glucose)The term “high-fructose corn syrup” is a little misleadingBecause corn syrup is 100% glucose, any presence of fructose typically results in it being labeled “high-fructose corn syrup”Soenen S, et al. Am J Clin Nutr. 2007;86(6): Smith JS, et al. Food Processing: Principles and Applications. Ames, IA: Blackwell Publishing; 2004, p
15 What Is the Potential Concern Regarding High-Fructose Corn Syrup? Animal and human studies using large amounts of fructose (generally > 17% of total energy), relative to the same amount of glucose, showIncreases in blood triglyceride levelsDecreased insulin sensitivityPossible increases in visceral adiposityPotential explanationsUnregulated metabolism of fructose increases de novo lipogenesisFructose, unlike glucose, does not generate an insulin responseInsulin may directly lower food intakeInsulin may increase leptin release from adipose tissue (leptin decreases food intake)Bantle JP, et al. Am J Clin Nutr. 2000;72(5):Stanhope KL, et al. J Clin Invest. 2009;119(5):
16 Keys to Making Sense of Fructose or High-Fructose Corn Syrup Literature Pure fructose versus high-fructose corn syrup is an important issueHuman studies have generally used pure fructose, not high-fructose corn syrup or sucroseIn preclinical studies, rodents have much greater ability for de novo lipogenesis from carbohydrates than do humansIn human studies, the level of fructose ingestion was at least double the current national average intakeSex differencesMen are more susceptible than women to the effects of fructose in blood lipids (ie, triglycerides)DiMeglio DP, et al. Int J Obesity. 2000;24: ; Melanson KJ, et al. Nutrition. 2007;23(2): ; Stanhope KL, et al. Am J Clin Nutr. 2008;87(5): ; Soenen S, et al. Am J Clin Nutr. 2007;86(6):
17 The Truth About High-Fructose Corn Syrup Too much sugar, of any kind, in beverages is not recommendedPoor compensation for carbohydrate energy consumed in beverages can lead to weight gainHowever, there are no differences in metabolic responses to high-fructose corn syrup and sucrose in humansNo differences in circulating hormonesNo differences in appetite or satiety-related variablesDiMeglio DP, et al. Int J Obesity. 2000;24: ; Melanson KJ, et al. Nutrition. 2007;23(2): ; Stanhope KL, et al. Am J Clin Nutr. 2008;87(5): ; Soenen S, et al. Am J Clin Nutr. 2007;86(6):
19 The Glycolysis Pathway Glucose (6 C)Glucokinase (liver)Hexokinase (muscle)aATPGlycogenADPGlucose-6-phosphateCytosolFructose-6-phosphateATPPhosphofructokinaseADPFructose-1,6-bisphosphate (6 C)Glyceraldehyde-3-phosphate (3C)DihydroxyacetonePhosphate (3C)Glyceraldehyde-3-phosphateNADNADPiPiNAD + H+NAD + H+1,3-bisphosphoglycerate1,3-bisphosphoglycerateADPADPATPATP3-phosphoglycerate3-phosphoglycerate2-phosphoglycerate2-phosphoglycerateH20H20Phosphoenolpyruvate (PEP)Phosphoenolpyruvate (PEP)PyruvatekinaseADPPyruvatekinaseADPATPATPPyruvate (3 C)Pyruvate (3 C)a For clarity, only selected enzymes are shown. Abbreviations: ADP, adenosine di phosphate; ATP, adenosine triphosphate; C, carbon; NAD, nicotinamide adenine dinucleotide; Pi, phosphate group. Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
20 Galactose and Glycolysis Galactose (Gal)Phosphorylated to galactose-1-phosphate (Gal-1-P) by galactokinaseGal-1-P converted to glucose-1-phosphate (Glc-1-P)Gal-1-P uridyl transferaseUridine diphosphogalactose 4-epimeraseGlc-1-P then enters glycolysis as does glucose derived from glycogenInborn errors of metabolismCan have inborn defects of the 3 enzymes of Gal metabolism (galactosemia)Results in accumulation of Gal in tissues such as lens of eye and damage (cataracts) due to osmotic effectGal-free diet requiredEffect of ethanolInhibits the epimerase enzymeAbbreviation: Glc, glucose.Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.Badawy AA-B. Alcohol and Alcoholism. 1977;12(3):
21 Fructose and Glycolysis Most is taken up by the liver and phosphorylated to fructose 1-phosphate (F-1-P) by fructokinaseAldolase B (liver form) splits F-1-P into glyceraldehyde and DHAPBoth can become glyceraldehyde-3-P (part of glycolytic pathway)Important that this enters glycolysis past PFK regulatory stepInborn errors of metabolismFructokinase defect (fructosuria)Not seriousAldolase B defectAccumulation of F-1-PDepletion of cellular phosphate storesBlocking of glycogen breakdown and gluconeogenesisFructose-free diet requiredAbbreviations: DHAP, dihydroxyacetone phosphate; PFK, phosphofructokinase.Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.Steinmann B, et al. Disorders of fructose metabolism. In: Scriver CR, Beaudet AL, Sly WS, Eds. The Metabolic and Molecular Bases of Inherited Disease. 8th ed. New York; McGraw Hill; 2001, p
22 Entry of Glucose, Galactose, and Fructose Into Liver Glycolysis Galactose-1-phosphateATPADPGalactokinaseUDP-glucose:uridyl transferaseUDP-glucoseUDP-galactoseUDP-glucose-4-epimeraseGlucoseATPADPGlucose-6-phosphateFructose-6-phosphateFructose-1,6-bisphosphateGlyceraldehyde-3-phosphateDihydroxyacetone phosphate+PhosphofructokinaseGlucose-1-phosphateFructoseFructokinaseFructose-1-phosphateAldolaseATPADPGlyceraldehyde+Dihydroxyacetone phosphateAbbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; UDP, uridine diphosphate.Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
23 Pentose Phosphate Pathway, or Hexose Monophosphate Shunt Alternative liver pathway for utilizing glucoseCan be used to generate ribose for nucleotide and ATP synthesisCan also serve as a source of NADPH for oxidation-reduction (redox) reactionsExample: reduction of glutathione to maintain stability of RBC membraneAbbreviations: ATP, adenosine triphosphate; NADPH, nicotinamide adenine dinucleotide phosphate; RBC, red blood cell.Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
24 GluconeogenesisAlmost a reversal of glycolysis, but must overcome thermodynamic barriers for 3 reactions:Glucokinase/hexokinasePhosphofructokinasePyruvate kinaseMethods of circumvention:Glucose-6-phosphataseFructose 1,6-bisphosphatasePyruvate carboxylase and phosphoenolpyruvate carboxykinase (PEPCK)Pyruvate carboxylase requires biotin as coenzymeBerg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
25 Gluconeogenesis in Liver GlucoseReactions different than glycolysisPiGlucose-6-phosphataseGlucose-6-phosphateFructose-6-phosphatePiFructose-1,6-bisphosphataseFructose-1,6-bisphosphateDihydroxyacetone-phosphateGlycerol-3-phosphateGlycerolGlycerol-3-phosphatePhosphoenolpyruvate (PEP)Phosphoenolpyruvatecarboxykinase (PEPCK)Amino acidsTCA cycleoxaloacetateAminoacidsAlaninePyruvatecarboxylasePyruvateLactateAbbreviations: TCA, tricarboxylic acid; Pi, phosphate group.Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
26 The Cori (Lactate) and Glucose-Alanine Cycles LiverBloodMuscleGlucoseGlucose-6-phosphateGlycogenGlycogenGlucose-6-phosphateUreaPyruvateLactateLactateLactatePyruvateNH2(eg, from leucine)NH2PyruvateAlanineAlanineAlanineAbbreviation: NH2, amino functional group.Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
27 GlycogenGlycogen is degraded by a different pathway than its synthesisKey enzyme for degradation is the activation of glycogen phosphorylaseVitamin B6 (pyridoxal phosphate) is a structural part of glycogen phosphorylaseSeveral types of glycogen storage disordersDeficiencies ofGlucose-6-phosphataseLysosomal alpha 1 4 and 1 6 glucosidase (acid maltase)Debranching enzymeMuscle phosphorylaseLiver phosphorylaseOthersBerg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
28 Glycogenesis/Glycogenolysis in Liver and Muscle (-1,4 and -1,6 glucose units)Branchingenzyme-1,4 glucose unitsUDPGlycogenphosphorylasePiGlycogensynthaseGlycogen primer+UDP-glucoseGlucan transferase/debranching enzymePPiUDPGlucose-1-phosphateATPADPGlucose-6-phosphateFree glucoseGlucose-6-phosphatase(liver only)Glucokinase (liver)Hexokinase (muscle)GlucoseAbbreviations: ADP, adenosine diphosphate; ATP, adenosine triphosphate; Pi, phosphate group; PPi, pyrophosphate; UDP, uridine diphosphate.Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman & Co.; 2002.
30 Storage of Carbohydrate in the Body Glucose that is absorbed, but not immediately needed, is stored as glycogenFound in the liver and skeletal musclesIt is similar to starchGlycogen in liver is a reserve glucose supply to the brainGlycogen in muscles is an energy source for exerciseGlycogen synthase in muscles is at peak activity immediately following glycogen-depleting exerciseEat carbohydrates immediately after exercise for most rapid glycogen replenishmentUnited States Anti-doping Agency. Optimal dietary intake guide. Available at: Accessed January 31, 2011.Berg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman and Co.; 2002.
31 Glycogen Distribution in the Body Liver60 to 120 g (4% to 8% of liver weight, overnight fasting versus fed, respectively)Liver glycogen is generally quite depleted by overnight fastingSkeletal muscle200 to 500 g (highly variable)Effects of training and carbohydrate loading on muscle glycogen storesUntrained, normal diet 80 to 90 mmol/kg muscle (wet weight)Trained, normal diet 130 to 135 mmol/kg muscle (wet weight)Trained, carbohydrate-loaded 210 to 230 mmol/kg muscle (wet weight)Coleman E. Today’s Dietitian. March 2002:15-18.Flatt JP. Am J Clin Nutr. 1995;61(suppl):952S-959S.
32 Glycogen Terminology Terms related to glycogen synthesis Glycogen synthase (enzyme that forms glycogen)Glycogenin (primer for glycogen synthesis)ProglycogenInitial phase of glycogen synthesis (glycogenin + small number of glucose molecules)MacroglycogenLarger ratio of glucose molecules to glycogeninForms to a greater extent vs proglycogen after 2 to 3 days of high-carbohydrate dietTerms related to glycogen breakdownGlycogen phosphorylaseBreaks down glycogen, with ultimate formation of glucose-6-phosphateGlucose-6-phosphataseNecessary to release the glucose from cell into bloodEnzyme is present in liver, absent in skeletal muscleMuscle glycogen for local use onlyBerg JM, et al. Biochemistry. 5th ed. New York, NY: WH Freeman and Co.; 2002.Huang M, et al. J Clin Invest. 1997;99(3):501–505. doi: /JCI
33 Muscle Glycogen Storage—Effects of Exercise KSPTRBRGDCAverage(N = 4)2.52.0Muscle Glycogen, g/100 g tissue1.51.00.5PREPOSTPREPOSTPREPOST5TH DAY POST10 miles10 miles10 milesDay 1Day 2Day 3Diet: carbohydrate, 40% to 50% kcals; fat, 30% to 40% kcals; protein, 10% to 15% kcals.Costill DL, et al. J Appl Physiol. 1971;31(6):
34 Factors Influencing Muscle Glycogen Synthesis Energy and CHO availabilityTiming of meals relative to completion of exercise (sooner the better)Additional protein possiblyGI of CHO (higher GI = faster)Degree to which glycogen is depleted (more depletion = faster)Rest (tapering of exercise is necessary)SexMen and women respond equally (ie, glycogen storage) if energy and CHO are adequateWomen seem to be less reliant on CHO and more reliant on fat during exercise than menAbbreviations: CHO, carbohydrate; GI, glycemic index.
35 Muscle Glycogen Storage— Effects of Diets With Differing CHO Levels Simple and complex CHO had equal glycogen resynthesis within the first 24 hours postexerciseComplex CHO had somewhat greater glycogen synthesis during subsequent 24 hours8070605040302010Change in Muscle Glycogen (mmol/kg muscle/24 hr)25%50%70%CHO diets, % of calories2 meals7 mealsa± SERunners performed glycogen-depleting exercise before dietary intakeDiets differed in percent of kcals from CHO, CHO type, and number of mealsAbbreviations: CHO, carbohydrate; SE, standard error. a Significant difference between the mean and the mean change in muscle glycogen observed during the mixed diet (50% of cal from CHO).Reprinted from Costill DL, et al. Am J Clin Nutr. 1981;34(9):
36 Can Protein Boost the Rate of Glycogen Storage? Mixed results in clinical studiesYesZawadski KM, et al. J Appl Physiol. 1992;72:Ivy JL, et al. J Appl Physiol. 2002;93:NoRoy BD, et al. J Appl Physiol. 1997;83:Jentjens RL, et al. J Appl Physiol. 2001;91:Van Hall G, et al. J Appl Physiol. 2000;88:Key issuesMore frequent feeding intervals did not show benefit with proteinAdequacy of carbohydrate and protein intakeProtein may be more important if athlete is unable to consume enough carbohydrate
37 Effect of Carbohydrate and Protein on Muscle Glycogen During Recovery 40a,b112 g CHO, 41 g protein112 g CHO41 g protein30aMuscle Glycogen Storage Rate, µmol/g pro/hour2010CHO-PROCHOPROSubjects ingested diet immediately and 2 hours after glycogen-depleting exercise; glycogen storage was assessed immediately and 4 hours postexercisea Significantly faster compared with PRO (P < .05).b Significantly faster compared with CHO (P < .05). Abbreviations: CHO, carbohydrate; Pro, protein.Zawadzki KM, et al. J Appl Physiol. 1992:72(5):
38 Muscle Glycogen Storage, mmol/L Effects of Carbohydrate-Protein Combination on Muscle Glycogen Storage During RecoveryminCHO-Pro: 80 g CHO, 28 g protein, 6 g fatHCHO: 108 g CHO, 6 g fatLCHO: 80 g CHO, 6 g fat60mina500-40 min40Muscle Glycogen Storage, mmol/L302010CHO-PROHCHOLCHOSubjects ingested diet immediately and 2 hours after glycogen-depleting exercise; glycogen storage was assessed immediately, at 20 and 40 minutes, and at 1, 2, 3, and 4 hours postexercisea Significantly higher compared with HCHO (P = .013) and LCHO (P = .004).Abbreviations: CHO, carbohydrate; Pro, protein; HCHO, high carbohydrate; LCHO, low carbohydrate. Reprinted from Ivy JL, et al. J Appl Physiol. 2002;93(4):
39 Muscle Glycogen Resynthesis With Different Diets After Exercise A diet of fat plus protein following exercise was not able to restore pre-exercise levels of muscle glycogen up to 4 days laterHowever, a carbohydrate diet restored muscle glycogen within 2 daysPre-Exe Post-Exe Post-ExeDay 19 am Immediate 5 pmDay 29 am 5 pmDay 39 amDay 4Day 5Day 6Day 7Day 8Day 9Subject 1DietFastingF+PCHOMG0.630.760.70Subject 184.108.40.2060.911.102.11Abbreviations: Exe, exercise; MG, muscle glycogen (g/100 g wet muscle tissue); F+P, 2000 kcal from fat and protein (<5% carbohydrate); CHO, 2000 kcal from carbohydrate ( 95% carbohydrate).Hultman E and Bergström J. Acta Med Scand. 1967;182(1):
40 Timing of Postexercise Carbohydrate Ingestion and Glycogen Resynthesis Maximal glycogen synthase is within 2 hours of exercise“Window of opportunity” to promote faster glycogen repletionGlycogen synthesis at 2 hours postexercise: more rapid with carbohydrate ingestion immediately postexercise vs carbohydrate ingestion delayed 2 hours postexerciseHowever, the delayed ingestion group can catch up within 24 hours given adequate carbohydrate intakeKey advantage of carbohydrate ingestion immediately postexercise is for athletes with multiple events in a short time spanNeed fast glycogen recoveryIvy JL, et al. J Appl Physiol. 1988;64(4): Parkin JA, et al. Med Sci Sports Exerc. 1997;29(2):Burke LM, et al. J Sports Sci. 2004;22:15-30.
41 Timing of Postexercise Carbohydrate Ingestion and Glycogen Resynthesis (continued) Immediate feedingDelayed feeding (2 hours)20402450100824Muscle Glycogen Storage, mmol/kg wet weight2Muscle Glycogen Storage, mmol/kg wet weight1P < .05NSTime Postexercise, hoursTime Postexercise, hours1. Ivy JL, et al. J Appl Physiol. 1988;64(4): Parkin JA, et al. Med Sci Sports Exerc. 1997;29(2):
42 Summary of Key Messages Carbohydrates are the major energy source for exercising muscleThe type of carbohydrate consumed influences the availability of energy to the muscleAbsorption and digestion are key stepsExcess carbohydrates in the body can be stored as glycogen for later muscle useA high-carbohydrate diet helps to maximize glycogen stores and generally increases exercise performancePostexercise meal content and timing can optimize glycogen resynthesis