L2. Exercise metabolism

Question 1

What is the main purpose of exercise metabolism?

Answer 1

To convert chemical energy into kinetic energy

Question 2

What are the key requirements for exercise metabolism?

Answer 2

Fuel availability, gas exchange, and circulation

Question 3

What is factorial aerobic scope?

Answer 3

The ratio of oxygen consumption at peak exercise to resting levels

Question 4

What limits exercise capacity during maximal efforts?

Answer 4

Fatigue, substrate stores, metabolic byproducts, or equipment failure

Question 5

What is the most energy-dense substrate in the body?

Answer 5

Fat, with 9.3 calories per gram

Question 6

Why is glycogen a less efficient energy store compared to fat?

Answer 6

Glycogen is stored with water, making it heavier per calorie

Question 7

What role do ketones play in exercise metabolism?

Answer 7

They act as a link between fat stores and brain energy needs

Question 8

What limits oxygen diffusion in the lungs during exercise?

Answer 8

Thickened alveolar-capillary barriers, such as in pulmonary fibrosis

Question 9

How does ventilation adapt to exercise?

Answer 9

Increases up to 17-fold to eliminate CO2

Question 10

What are the immediate energy sources for muscle contraction?

Answer 10

Phosphocreatine and ATP

Question 11

What energy system supports fast ATP production without oxygen?

Answer 11

Anaerobic glycolysis

Question 12

What is the TCA cycle, and why is it essential?

Answer 12

It is the citric acid cycle responsible for oxidative metabolism of substrates

Question 13

What experiment demonstrated muscle glycogen depletion?

Answer 13

Bergstrom and Hultman’s 1966 study with one-legged cycling and biopsies

Question 14

What is the role of glycogen in fat oxidation?

Answer 14

Glycogen provides intermediates needed for the TCA cycle to oxidize fat

Question 15

Why does hitting the wall occur in endurance events?

Answer 15

Depleted glycogen prevents the regeneration of TCA cycle intermediates

Question 16

What is anaplerosis?

Answer 16

The replenishment of TCA cycle intermediates from other substrates

Question 17

How do phosphocreatine stores replenish during exercise?

Answer 17

Through ATP generated via oxidative phosphorylation

Question 18

What substrate contributes most to energy during submaximal exercise?

Answer 18

Free fatty acids

Question 19

What determines the predominant energy substrate during exercise?

Answer 19

Exercise intensity and duration

Question 20

What is the role of type I muscle fibers in exercise?

Answer 20

They support endurance activities using oxidative metabolism

Question 21

Why are type IIx muscle fibers important for sprinting?

Answer 21

They support fast and forceful contractions using glycolysis

Question 22

What is the significance of PEPCK in metabolism?

Answer 22

It facilitates the shuttling of carbons into TCA cycle intermediates

Question 23

What experiment highlighted fat burning in the presence of carbohydrates?

Answer 23

Knox and colleagues’ 1948 rabbit kidney and fumarate study

Question 24

Why do some athletes train in a low-carbohydrate state?

Answer 24

To upregulate fat oxidation pathways for endurance

Question 25

What limits sprint performance physiologically?

Answer 25

Speed and force of contraction of fast-twitch muscle fibers

Question 26

How do athletes optimize glycogen stores?

Answer 26

By carbohydrate loading after exhaustive exercise

Question 27

What happens to lactate during low-intensity exercise?

Answer 27

It is oxidized by type I fibers or recycled by the liver into glucose

Question 28

What role does the liver play in exercise metabolism?

Answer 28

Recycling lactate into glucose via the Cori cycle

Question 29

What adaptation allows endurance athletes to burn more fat?

Answer 29

Increased mitochondrial density and fat oxidation capacity

Question 30

How does exercise intensity affect fuel utilization?

Answer 30

Higher intensities increase reliance on glycogen and glucose

Question 31

Why is fat a better energy store for mobility?

Answer 31

It is lightweight and energy-dense compared to glycogen

Question 32

What experiment demonstrated the role of TCA intermediates in oxidation?

Answer 32

Cold-fasted rat liver extracts improved fatty acid oxidation

Question 33

What is the primary limiting factor in submaximal endurance exercise?

Answer 33

Carbohydrate availability for anaplerosis

Question 34

What are carbohydrate response elements?

Answer 34

Transcriptional regulators promoting fat oxidation under low-carb conditions

Question 35

What did Romijn's study reveal about exercise metabolism?

Answer 35

Fuel source transitions from fats to carbohydrates as exercise intensity rises

Question 36

Why does glycogen depletion not mean running out of fuel?

Answer 36

Fat stores remain abundant but cannot sustain the TCA cycle alone

Question 37

What limits oxidative capacity when glycogen is depleted?

Answer 37

Exhaustion of anaplerotic TCA intermediates

Question 38

How does the heart contribute to fuel selection during exercise?

Answer 38

It preferentially oxidizes lactate and free fatty acids

Question 39

Why are ketones less relevant in modern human metabolism?

Answer 39

Frequent feeding suppresses ketogenesis and reliance on ketones

Question 40

What is the relationship between carbon dioxide production and ventilation during exercise?

Answer 40

Ventilation increases to eliminate carbon dioxide produced during metabolism