Interactions Interactions Between Muscle Between Muscle

Glycogen and Blood Glycogen and Blood Glucose Glucose

During ExerciseDuring ExerciseA Review by Mark A Review by Mark

Hargreaves, Hargreaves,

Presented by Anna ZornPresented by Anna Zorn

ObjectivesObjectives Discuss primary CHO forms of fuel Discuss primary CHO forms of fuel

during exerciseduring exercise Review major CHO sourcesReview major CHO sources Explore glycogen as an exercise Explore glycogen as an exercise

fuelfuel Explore glucose as an exercise fuelExplore glucose as an exercise fuel ““The Big Picture”: CHO interactionThe Big Picture”: CHO interaction View hypotheses regarding CHO-View hypotheses regarding CHO-

ingestioningestion

Exercise FuelExercise Fuel

Powers & Howley, Figure 4-11

Exercise FuelExercise Fuel

Powers & Howley, Figure 4-13

CarbohydratesCarbohydrates

FORMS: FORMS: Muscle GlycogenMuscle Glycogen Blood GlucoseBlood Glucose

SOURCES: SOURCES: Glycogenesis: glycogen synthesisGlycogenesis: glycogen synthesis Glycogenolysis: glycogen degradationGlycogenolysis: glycogen degradation Gluconeogenesis: glucose synthesisGluconeogenesis: glucose synthesis Dietary intake: Glucose absorption Dietary intake: Glucose absorption

via intestinesvia intestines

Muscle GlycogenolysisMuscle Glycogenolysis Glycogen Degradation: Glycogen Degradation:

Glycogen phosphorylase: regulatory Glycogen phosphorylase: regulatory enzymeenzyme Activation:Activation:

Glucagon / Epinephrine – Glucagon / Epinephrine – Response to low BGResponse to low BG

Cascade amplificationCascade amplification High Ca2+ concentrationsHigh Ca2+ concentrations

Inactivation: Inactivation: Insulin – Response to high BGInsulin – Response to high BG

Muscle Glycogenolysis

Metabolism, Figure 12-7

Muscle Glycogen Muscle Glycogen DegradationDegradation

Activators of Activators of GlycogenolysisGlycogenolysis

Allosteric ActivatorsAllosteric Activators: reflect intracellular : reflect intracellular energyenergy ADP, PiADP, Pi

More bi-products = More bi-products = ↑↑ energy energy demanddemand

Intense exercise = Intense exercise = ↑↑ATP turnover, ATP turnover, ↑↑ allosteric activators. allosteric activators. ↑↑ activation of GP activation of GP

Other Activators:Other Activators: ↓ ↓ FFA in plasma = FFA in plasma = ↑↑ glycogen glycogen

degradationdegradation ↑ ↑ GGlycogen = lycogen = ↑ G↑ Glycogenolysis lycogenolysis

Inhibition of Inhibition of GlycogenolysisGlycogenolysis

Allosteric InhibitorsAllosteric Inhibitors:: ATP, NADHATP, NADH

↓↓ intracellular energy demand intracellular energy demand = = ↓ GP ↓ GP

Other Inhibitors:Other Inhibitors: ↑↑ FFA in plasma: FFA in plasma: ↓↓ rate of rate of

glycogenolysis glycogenolysis ↓↓ Glycogen = Glycogen = ↓↓ Glycogenolysis Glycogenolysis

GluconeogenesisGluconeogenesis

Figure 9-2: metabolism pg. 131Figure 9-2: metabolism pg. 131

Metabolism, Figure 9-2

Glucose UptakeGlucose Uptake

Facilitation of Glucose Uptake:Facilitation of Glucose Uptake: Insulin + GlucoseInsulin + Glucose

Insulin binds to insulin receptor Insulin binds to insulin receptor Glucose binds with GLUT-4Glucose binds with GLUT-4

Muscle contractions Muscle contractions Exercise = increased blood flowExercise = increased blood flow GLUT– 4 Translocation = movement GLUT– 4 Translocation = movement

of transport protein from of transport protein from intracellular site to membraneintracellular site to membrane

Glucose UptakeGlucose Uptake

Increased muscle glucose uptake Increased muscle glucose uptake and GLUT-4 translocation (due to and GLUT-4 translocation (due to exercise) increase exercise) increase with or without with or without insulin!insulin!

Effects of insulin and exercise on Effects of insulin and exercise on glucose uptake are additive.glucose uptake are additive.

Local factors (Intracellular) are Local factors (Intracellular) are more influential in glucose uptake more influential in glucose uptake than systemic factors (circulatory)than systemic factors (circulatory)

““The Big Picture”The Big Picture”

Glycogen / Glucose Utilization Are Glycogen / Glucose Utilization Are Affected ByAffected By

Exercise DurationExercise Duration

Exercise IntensityExercise Intensity

Glycogen and Glucose AvailabilityGlycogen and Glucose Availability

Availability of other fuels (FFA)Availability of other fuels (FFA)

““The Big Picture”The Big Picture”

Exercise of Increasing Duration:Exercise of Increasing Duration: Onset: Glycogen depletion is most rapid Onset: Glycogen depletion is most rapid

now accounting for most of CHO now accounting for most of CHO oxidation.oxidation.

Glycogenolysis continues to Glycogenolysis continues to substantially contribute as long as substantially contribute as long as intensity is low. With time, glycogen intensity is low. With time, glycogen depletes and less glycogenolysis occurs.depletes and less glycogenolysis occurs.

Glucose uptake increases with time, and Glucose uptake increases with time, and more is utilized as exercise time more is utilized as exercise time progresses and glycogen depletes.progresses and glycogen depletes.

““The Big Picture”The Big Picture”

Exercise of Increasing Intensity:Exercise of Increasing Intensity: Low:Low: Relatively low glucose uptake, but Relatively low glucose uptake, but

high utilization. Muscle glycogen high utilization. Muscle glycogen degradation is low.degradation is low.

Moderate:Moderate: Moderate rate of glucose Moderate rate of glucose uptake and utilization. Relatively uptake and utilization. Relatively greater glycogen degradation.greater glycogen degradation.

High:High: High rate of glucose uptake, but High rate of glucose uptake, but little utilization. Quick rate of little utilization. Quick rate of glycogenolysis.glycogenolysis.

Carbohydrate IngestionCarbohydrate Ingestion

CHO – LoadingCHO – Loading CHO – SupplementationCHO – Supplementation

CHO AS AN ERGOGENIC AID? CHO AS AN ERGOGENIC AID? Varying ResultsVarying Results Depends on exercise duration, Depends on exercise duration,

intensity, and modeintensity, and mode

Research ConclusionsResearch Conclusions The interaction between glycogen and The interaction between glycogen and

glucose fuel is complex, and even more glucose fuel is complex, and even more so regarding exercise.so regarding exercise.

Muscle glycogen influences muscle Muscle glycogen influences muscle glucose uptake.glucose uptake.

Glucose uptake increases when muscle Glucose uptake increases when muscle glycogen decreases.glycogen decreases.

Prolonged exercise = more glucose Prolonged exercise = more glucose uptake as glycogen decreases from uptake as glycogen decreases from glycogenolysis.glycogenolysis.

These relationships have not been These relationships have not been proven causal.proven causal.

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