Exercise Physiology: Fuel Selection and Muscle Fibers

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Questions and Answers

Which factor has the greatest influence on fuel selection during exercise?

Feeding and nutritional status

Exercise intensity (correct)

Prior exercise and training status

Muscle acidity

What is the role of AMP in relation to fuel use during exercise?

AMP indicates energy depletion and stimulates catabolism of fuels (correct)

AMP promotes aerobic metabolism exclusively

AMP decreases muscle acidity, enhancing fuel availability

AMP solely regulates blood flow during high-intensity workouts

In terms of energy contribution, what is the primary energy system utilized in BMX racing?

50% Aerobic and 50% Anaerobic

100% Anaerobic (correct)

70% Aerobic and 30% Anaerobic

100% Aerobic

Which of the following best describes the relationship between exercise duration and fuel use?

Fuel use becomes limited by oxygen availability in prolonged activities Signup and view all the answers

Which factor does NOT primarily influence fuel availability during physical activity?

Current fatigue level of the athlete Signup and view all the answers

At what intensity percentage of VO2max does muscle glycogen usage peak in comparison to other fuels?

75% Signup and view all the answers

What is the primary fuel source used during high-intensity exercise as expressed by energy use in kcal/min?

Blood Glucose Signup and view all the answers

Which muscle fiber type is characterized by a good blood supply and many mitochondria?

Type I Signup and view all the answers

How does the Respiratory Exchange Ratio (RER) behave during low-intensity exercise?

RER ranges approximately between 0.7 and 0.85 Signup and view all the answers

Which fuel source provides a higher proportion of energy during low-intensity exercise compared to high-intensity exercise?

Blood Fatty Acids Signup and view all the answers

What is the primary source of energy in the initial stages of exercise before glycogen stores are depleted?

Glucose Signup and view all the answers

Which factor contributes to a greater reliance on fat for fuel in trained athletes at high exercise intensities?

Greater intramuscular triglyceride (IMTG) stores Signup and view all the answers

What does the phrase 'fat burns in a carbohydrate flame' imply about fat oxidation?

Oxaloacetate from carbohydrates is essential for complete fat oxidation Signup and view all the answers

What is the role of the enzyme PDH in the context of exercise metabolism?

It regulates glucose metabolism to help save glycogen stores Signup and view all the answers

How does carbohydrate ingestion during prolonged exercise benefit performance?

It allows for longer duration performance at higher intensities and delays fatigue Signup and view all the answers

Study Notes

Fuel Selection during Exercise

Exercise duration and intensity are key factors affecting fuel selection.
Higher intensities rely more on carbohydrate, while longer durations rely more on fat.
Muscle glycogen and blood glucose are the primary sources for higher intensity exercise.
Blood fatty acids and muscle triglycerides are the primary sources for lower intensity, prolonged exercise.
RER (Respiratory Exchange Ratio) indicates fuel use: lower RER indicates fat oxidation, higher RER indicates carbohydrate oxidation.
As exercise intensity increases, the contribution of carbohydrate increases.

Muscle Fiber Types

Type I fibers (slow twitch) have more mitochondria and better blood supply, supporting aerobic metabolism.
Type IIb fibers (fast twitch) have fewer mitochondria and poorer blood supply, supporting anaerobic metabolism.

Glycogen Depletion

Glycogen depletion occurs faster during higher intensity exercise due to increased rate of glycolysis.
Initially, glucose is used, then fatty acids take over and glucose is recycled.
Muscle glycogen stores are limited, while fat stores are much larger.

Regulation of Fuel Use

PDH activity regulates entry of pyruvate into the mitochondria, controlling carbohydrate oxidation.
High levels of acetyl-CoA inhibit PDH activity, reducing carbohydrate oxidation and favoring fat oxidation.
Hormones such as adrenaline, insulin, and cortisol play a role in regulating both fat and carbohydrate metabolism.
Adrenaline and insulin stimulate glucose uptake, while cortisol increases lipolysis and gluconeogenesis.

Example Exam Question:

Moderate intensity exercise utilizes both aerobic and anaerobic systems, with a higher reliance on aerobic metabolism.
The primary energy system is likely aerobic and the primary fuel sources are likely a mix of carbohydrates (glycogen and glucose) and fat.
**Mechanisms regulating fuel use include:
- Hormonal regulation: increased catecholamines and glucagon stimulate glycogen breakdown and fatty acid mobilization.
- Substrate availability: limited blood flow to adipose tissue leads to a greater reliance on intramuscular triglycerides and glycogen.

Maximal Fat Oxidation

Maximal fat oxidation occurs at around 65% of VO2max.

Catecholamines and Fat Oxidation

High levels of catecholamines during high-intensity exercise increase lipolysis, but also increase the rate of carbohydrate oxidation, reducing the net effect of fat oxidation.

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Description

Explore the crucial relationship between exercise duration, intensity, and fuel selection in this quiz. Learn how different muscle fiber types contribute to exercise performance and the impact of glycogen depletion on higher intensity workouts. Test your understanding of aerobic and anaerobic metabolism.