Fuel Utilization

Question 1

Sources of Fuel During Exercise

Answer 1

Carbohydrate: (Blood glucose, muscle glycogen)
Fat: Plasma FFA (from adipose tissue lipolysis)
Intramuscular triglycerides
Protein: Only a small contribution to total energy production (-2%). May increase 5-15% late in prolonged exercise
Blood Lactate: Via cori cycle

Question 2

ATP-PC System (Rate Limiting Enzyme, Stimulators, Inhibitors)

Answer 2

1. Creatine Kinase
2. ADP
3. ATP

Question 3

Glycolysis ((Rate Limiting Enzyme, Stimulators, Inhibitors)

Answer 3

1. Phosphofructokinase
2. AMP, ADP, Pi, increase in ph
3. ATP, CP, citrate, decrease in ph

Question 4

Krebs Cycle (Rate Limiting Enzyme, Stimulators, Inhibitors)

Answer 4

1. Isocitrate Dehydrogenase
2. ADP, Ca, NAD
3. ATP, NADH

Question 5

Electron Transport Chain ((Rate Limiting Enzyme, Stimulators, Inhibitors)

Answer 5

1. Cytochrome Oxidase
2. ADP, Pi
3. ATP

Question 6

Respiratory Exchange Ratio

Answer 6

R= VCO2/VO2

0. 8 normal value
1. 15 standard for exercise because respiring more CO2

Normally starts around 1 then drops to .7/.8 then goes up incrementally

Question 7

R for Fat (100%)

Answer 7

0.7 (4.7 kcal/l)

Question 8

R for Carbohydrate (100%)

Answer 8

1.0 (5.0 kcal/L)

Question 9

R for 50/50 Carb and Fat

Answer 9

0.85 (4.86 kcal/l)

Question 10

In order for R to be used an estimate of Substrate Utlization during exercise

Answer 10

Subject must be in steady state

Only during steady state are VCO2 and VO2 reflective of metabolic exchange of gases in tissues.

Question 11

Exercise Intensity and Fuel Selection: Low Intensity Exercise (<30% VO2 max)

Answer 11

Fats are primary fuel during prolonged low intensity exercise

Question 12

Exercise Intensity and Fuel Selection: High Intensity Exercise (<70% VO2 max)

Answer 12

Carbohydrates primary fuel

Question 13

Exercise Intensity and Fuel Selection: Crossover Concept

Answer 13

Describes shift from fat to CHO metabolism as exercise intensity increases

Results from: Recruitment of fast muscle fibers
Increasing blood levels of epinephrine.

Occurs around 35% VO2 max

Question 14

McArdle’s Syndrome

Answer 14

Genetic error in muscle glycogen metabolism
Cannot synthesize the muscle enzyme phosphorylase due to a gene mutation; results in an inability to break down muscle glycogen
Patients do not produce lactate during an incremental exercise test and complain of exercise intolerance and muscle pain.

Question 15

Low Exercise Intensities (20% VO2 max)

Answer 15

High percentage of energy expenditure (66%) derived from fat
Total energy expended is low (3 kcal min)
Total fat oxidation is also low (2 kcal min)

Question 16

FATmax

Answer 16

Highest rate of fat oxidation

Reached just before lactate threshold

Question 17

Higher Exercise Intensities (60% VO2 max)

Answer 17

Lower percentage of energy (33%) from fat
Total energy expended is higher (9 kcal min)
Total fat oxidation is also higher (3 kcal min)

Question 18

Prolonged low-intensity exercise

Answer 18

Shift from carbohydrate metabolism toward fat metabolism (training makes this transition faster)

Results from an increase in lipolysis (Breakdown of triglycerides-> glycerol + FFA) by enzymes called lipases

Stimulated by an increase in blood level epinephrine.

Question 19

Prolonged High intensity exercise

Answer 19

Glycogen is depleted because:

Reduced rate of glycolysis and production of pyruvate
Reduced citric acid (Krebs cycle intermediates
Reduced fat oxidation (Fats metabolized by Krebs cycle)

Question 20

Ingestion of Carbohydrates during endurance activity

Answer 20

Improves endurance performance as depletion of muscle and blood carbohydrate stores contributes to fatigue

True during submaximal (<70% VO2 max), long duration (>90 minutes) exercise.
30-60 g carbohydrate required.
May also improve performance in shorter, higher intensity events (45 minutes duration).

Question 21

Muscle Glycogen

Answer 21

Primary source of carbohydrate during high intensity exercise
Supplies much of the carbohydrate in first hour of exercise

Question 22

Blood Glucose

Answer 22

From liver glycogenolysis
Primary source of CHO during low intensity exercise
Important during long duration exercise (As muscle glycogen levels decline)

Question 23

Intramuscular Triglycerides

Answer 23

Primary source of fat during higher intensity exercise

Question 24

Plasma FFA

Answer 24

from adipose tissue lipolysis (Triglycerides -> glycerol + FFA)
FFA concerted to acetyl-CoA and enters citric acid cycle
Primary source of fat during low intensity exercise
Becomes more important as muscle triglyceride levels decline in long duration exercise

Question 25

Sources of Protein During Exercise

Answer 25

Broken down into amino acids

Muscle can metabolize branch chain amino acids and alanine
Liver can convert alanine to glucose

Question 26

Protein contribution to total energy production

Answer 26

Small (only 2%)
May increase to 5-10% late in prolonged duration exercise

Enzymes that degrade proteins (proteases) are activated in long term exercise.

Question 27

Lactate as a Fuel Source during exercise

Answer 27

Can be used by skeletal muscle and heart (Converted to acetyl-CoA and enters krebs cycle)

Can be converted to glucose in liver (Cori Cycle)

Lactate shuttle: lactate produced in one tissue and transported to another

Question 28

Cori Cycle

Answer 28

Lactate produced by skeletal muscle is transported to liver
Liver converts lactate to glucose (gluconeogenesis)
Glucose is transported back to muscle and used as fuel