Chpt 4 Study Questions

Question 1

Identify the predominant energy systems used to produce ATP during the following types of exercise

a. Short-term, intense exercise (i.e., less than 10seconds’ duration)

b. 400-meter dash

c. 20-kilometer race (i.e., 12.4 miles)

Answer 1

A: Anaerobic; ATP-PC and glycolysis

B: Mainly anaerobic through ATP-PC and some aerobic

C: Aerobic because long duration of time

Question 2

Where does the ATP come from during the transition period from rest to steady state?

Answer 2

-ATP produced through anaerobic pathways; ATP-PC system and glycolysis.

-Once steady state is reached, ATP requirement met through aerobic pathways

Question 3

How does the modern theory of EPOC differ from the classical oxygen debt theory proposed by A. V. Hill?

Answer 3

-Classical theory: majority of lactic acid converted to glucose in liver.

-Modern theory:
1. 70% of lactic acid is oxidized & used as a substrate by heart and skeletal muscle

2.20% converted to glucose

3.10% converted to amino acids

Question 4

Discuss several possible reasons why blood lactate begins to rise rapidly during incremental exercise.

Answer 4

-Due to increase in % VO2 max. Increased use of oxygen and fast-twitch muscle fibers leads to build up of lactic acid because NADH produced faster than utilized.

-Due to increase in anaerobic metabolism, which causes low O2 levels

Question 5

Briefly explain how the respiratory exchange ratio is used to estimate which substrate is being utilized during exercise.

Answer 5

• The subject must have reached steady state.
• Ratio of VCO2:VO2; fat consumes more oxygen and produces more CO2
• RER of 0.7 means fat utilzation is dominant and RER of 1.0 means carbs utilization is dominant.

Question 6

What is meant by the term nonprotein R?

Answer 6

• The role that protein contributes to ATP production during exercise is ignored because protein plays a small role as a substrate during physical activity (~2%)
• Enzymes that degrade proteins (proteases) are activated in long-term exercise

Question 7

List the factors that play a role in the regulation of carbohydrate metabolism during exercise.

Answer 7

• Recruitment of fast-twitch muscle fibers
• Increasing blood levels of epinephrine

Question 8

Discuss the importance of exercise intensity on muscle fuel selection.

Answer 8

• Fats (FFA) and Carbs (blood glucose) are primary fuel source during low intensity exercise (<30% VO2 max)
• Carbs (muscle glycogen) and fats (muscle triglycerides) are primary fuel source during high intensity exercise (>70% VO2 max)
• As intensity increases, there is an increase in carb metabolism and decrease in fat metabolism; called the crossover concept

Question 9

How does the duration of exercise influence muscle fuel selection?

Answer 9

• Prolonged, low intensity exercise causes shift from carb metabolism (blood glucose) to fat metabolism.

a. Due to increased rate of lipolysis creating FFA; stimulated by rising blood levels of epinephrine

• Shorter, higher intensity exercise uses carbs (muscle glycogen) as major fuel source and muscle triglycerides.

Question 10

List those variables that regulate fat metabolism during exercise.

Answer 10

• Intensity and duration
• Diet
• Blood levels of epinephrine and NE
• Levels of intramuscular triglycerides
• Plasma FFA from adipose tissue lipolysis

Question 11

What is the “lactate shuttle”?

Answer 11

• Lactate produced in one tissue and transported to another

a. Can be converted to glucose in liver by the Cori cycle

b. Lactate produced by muscles transported to liver

c. Liver converts lactate to glucose

d. Glucose transported back to muscle and used as fuel

• Lactate can be used as fuel source by skeletal muscles and heart

a. Converted to acetyl-CoA and enters krebs cycle

Question 12

What does cause muscle soreness?

Answer 12

-Microscopic injury to muscle fibers leads to inflammation

Question 13

Is Low-Intensity Exercise Best for Burning Fat?

Answer 13

• At low exercise intensities (~20% VO2 max), total fat oxidation is also low (2 kcal*min-1).
• At higher exercise intensities (~60% VO2 max), total fat oxidation is also higher (3 kcal*min-1).
• FATmax: reached just before lactate threshold

Question 14

McArdle’s Syndrome

Answer 14

• Cannot synthesize the enzyme phosphorylase
• Inability to break down muscle glycogen. Also prevents lactate production
• Patients complain of exercise intolerance and muscle pain