Chapter 4: Exercise Metabolism

Question 1

What happens to ATP demand and O₂ consumption at the onset of exercise?

Answer 1

ATP demand increases instantly, O₂ consumption increases gradually

This transition leads to an aerobic steady state achieved within 1-4 minutes.

Question 2

What is Oxygen Deficit?

Answer 2

Lag in oxygen uptake observed at onset of exercise

It is the difference between oxygen uptake in the first few minutes vs. steady state.

Question 3

How does the oxygen deficit differ between trained and untrained individuals?

Answer 3

Trained individuals have a smaller O₂ deficit and quicker steady state

This indicates better efficiency in oxygen utilization.

Question 4

What does EPOC stand for?

Answer 4

Excess Post-Exercise Oxygen Consumption

It refers to elevated O₂ consumption after exercise.

Question 5

What are the causes of EPOC?

Answer 5

• Lactate to glucose conversion
• Restoration of PCr and O₂ stores
• Sustained increased heart/breathing rate
• Elevated body temperature
• Elevated hormone circulation

Greater EPOC occurs after high-intensity exercise.

Question 6

What is the physiological ceiling for the oxygen transport system?

Answer 6

VO₂max

It is the maximal volume of oxygen the body can consume, distribute, and utilize.

Question 7

What are the primary criteria for reaching VO₂max?

Answer 7

• Plateau (<150 mL/min increase despite increasing workload)
• Age-predicted HRmax ±10 bpm
• RPE ≥17
• RER ≥1.1
• Blood lactate ≥8 mmol/L

These criteria help assess if VO₂max has been achieved.

Question 8

What is the Lactate Threshold (LT)?

Answer 8

Work rate at which blood lactate rises systematically during incremental exercise

It varies between trained and untrained individuals.

Question 9

What is the typical Lactate Threshold for untrained individuals?

Answer 9

50-60% VO₂max

This indicates the intensity at which lactate begins to accumulate in the blood.

Question 10

What mechanisms can lead to an increased lactate production?

Answer 10

• Low muscle oxygen (hypoxia)
• Accelerated glycolysis (NADH produced faster than used)
• Recruitment of fast-twitch muscle fibers
• Reduced lactate removal from blood

These factors contribute to the lactate threshold response.

Question 11

How is lactate removed after exercise?

Answer 11

• 70% oxidized by cells (heart and skeletal muscle)
• 20% converted to glucose
• 10% converted to amino acids

This illustrates the body’s recovery mechanism post-exercise.

Question 12

What does the Respiratory Exchange Ratio (RER) indicate?

Answer 12

RER = VCO₂/VO₂

It is used to estimate fuel utilization during exercise.

Question 13

What does an RER of 0.7 indicate?

Answer 13

100% fat utilization

This ratio helps in understanding which fuel source the body is predominantly using.

Question 14

What is the ‘crossover point’ in exercise physiology?

Answer 14

Shift from fat to CHO as primary fuel

This occurs as exercise intensity increases.

Question 15

What are the primary carbohydrate sources during high-intensity exercise?

Answer 15

• Muscle glycogen
• Blood glucose (from liver glycogenolysis)

These sources are crucial for energy during intense physical activity.

Question 16

What are the fat sources utilized during low-intensity exercise?

Answer 16

• Intramuscular triglycerides
• Plasma Free-Fatty Acids

These fats serve as primary energy sources at lower intensities.

Question 17

What is the contribution of protein to energy production during exercise?

Answer 17

Small contribution (~2-10%)

BCAAs can be metabolized directly in muscle for energy.

Question 18

What role does lactate play in muscle metabolism?

Answer 18

Can be direct fuel for slow muscle fibers and heart

Lactate can also be converted to glucose in the liver (Cori Cycle).