Interactions Between
Muscle Glycogen and
Blood Glucose
During Exercise
A Review by Mark Hargreaves,
Presented by Anna Zorn
Objectives
Discuss primary CHO forms of fuel
during exercise
 Review major CHO sources
 Explore glycogen as an exercise fuel
 Explore glucose as an exercise fuel
 “The Big Picture”: CHO interaction
 View hypotheses regarding CHOingestion

Exercise Fuel
Powers & Howley, Figure 4-11
Exercise Fuel
Powers & Howley, Figure 4-13
Carbohydrates

FORMS:
Muscle Glycogen
 Blood Glucose


SOURCES:
Glycogenesis: glycogen synthesis
 Glycogenolysis: glycogen degradation
 Gluconeogenesis: glucose synthesis
 Dietary intake: Glucose absorption via
intestines

Muscle Glycogenolysis

Glycogen Degradation:

Glycogen phosphorylase: regulatory enzyme
 Activation:
 Glucagon / Epinephrine – Response to
low BG
 Cascade amplification
 High Ca2+ concentrations
 Inactivation:
 Insulin – Response to high BG
Muscle Glycogenolysis
Metabolism, Figure 12-7
Muscle Glycogen Degradation
Activators of Glycogenolysis

Allosteric Activators: reflect intracellular energy
 ADP, Pi



More bi-products = ↑ energy demand
Intense exercise = ↑ATP turnover, ↑ allosteric
activators. ↑ activation of GP
Other Activators:
↓ FFA in plasma = ↑ glycogen degradation
 ↑ Glycogen = ↑ Glycogenolysis

Inhibition of Glycogenolysis

Allosteric Inhibitors:


ATP, NADH
 ↓ intracellular energy demand = ↓ GP
Other Inhibitors:


↑ FFA in plasma: ↓ rate of glycogenolysis
↓ Glycogen = ↓ Glycogenolysis
Gluconeogenesis

Figure 9-2: metabolism pg. 131
Metabolism, Figure 9-2
Glucose Uptake

Facilitation of Glucose Uptake:

Insulin + Glucose
 Insulin binds to insulin receptor
 Glucose binds with GLUT-4

Muscle contractions
 Exercise = increased blood flow
 GLUT– 4 Translocation = movement of
transport protein from intracellular site to
membrane
Glucose Uptake
Increased muscle glucose uptake and
GLUT-4 translocation (due to exercise)
increase with or without insulin!
 Effects of insulin and exercise on glucose
uptake are additive.
 Local factors (Intracellular) are more
influential in glucose uptake than systemic
factors (circulatory)

“The Big Picture”

Glycogen / Glucose Utilization Are Affected By

Exercise Duration

Exercise Intensity

Glycogen and Glucose Availability

Availability of other fuels (FFA)
“The Big Picture”

Exercise of Increasing Duration:

Onset: Glycogen depletion is most rapid now
accounting for most of CHO oxidation.
 Glycogenolysis
continues to substantially
contribute as long as intensity is low. With time,
glycogen depletes and less glycogenolysis
occurs.
 Glucose
uptake increases with time, and more is
utilized as exercise time progresses and glycogen
depletes.
“The Big Picture”

Exercise of Increasing Intensity:
Low: Relatively low glucose uptake, but high
utilization. Muscle glycogen degradation is low.
 Moderate: Moderate rate of glucose uptake and
utilization. Relatively greater glycogen
degradation.
 High: High rate of glucose uptake, but little
utilization. Quick rate of glycogenolysis.

Carbohydrate Ingestion

CHO – Loading
CHO – Supplementation

CHO AS AN ERGOGENIC AID?

Varying Results
 Depends on exercise duration, intensity, and
mode

Research Conclusions
The interaction between glycogen and glucose
fuel is complex, and even more so regarding
exercise.
 Muscle glycogen influences muscle glucose
uptake.
 Glucose uptake increases when muscle glycogen
decreases.
 Prolonged exercise = more glucose uptake as
glycogen decreases from glycogenolysis.
 These relationships have not been proven causal.

References
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