Fuel Utilization Flashcards
Sources of Fuel During Exercise
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
ATP-PC System (Rate Limiting Enzyme, Stimulators, Inhibitors)
- Creatine Kinase
- ADP
- ATP
Glycolysis ((Rate Limiting Enzyme, Stimulators, Inhibitors)
- Phosphofructokinase
- AMP, ADP, Pi, increase in ph
- ATP, CP, citrate, decrease in ph
Krebs Cycle (Rate Limiting Enzyme, Stimulators, Inhibitors)
- Isocitrate Dehydrogenase
- ADP, Ca, NAD
- ATP, NADH
Electron Transport Chain ((Rate Limiting Enzyme, Stimulators, Inhibitors)
- Cytochrome Oxidase
- ADP, Pi
- ATP
Respiratory Exchange Ratio
R= VCO2/VO2
- 8 normal value
- 15 standard for exercise because respiring more CO2
Normally starts around 1 then drops to .7/.8 then goes up incrementally
R for Fat (100%)
0.7 (4.7 kcal/l)
R for Carbohydrate (100%)
1.0 (5.0 kcal/L)
R for 50/50 Carb and Fat
0.85 (4.86 kcal/l)
In order for R to be used an estimate of Substrate Utlization during exercise
Subject must be in steady state
Only during steady state are VCO2 and VO2 reflective of metabolic exchange of gases in tissues.
Exercise Intensity and Fuel Selection: Low Intensity Exercise (<30% VO2 max)
Fats are primary fuel during prolonged low intensity exercise
Exercise Intensity and Fuel Selection: High Intensity Exercise (<70% VO2 max)
Carbohydrates primary fuel
Exercise Intensity and Fuel Selection: Crossover Concept
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
McArdle’s Syndrome
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.
Low Exercise Intensities (20% VO2 max)
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)
FATmax
Highest rate of fat oxidation
Reached just before lactate threshold
Higher Exercise Intensities (60% VO2 max)
Lower percentage of energy (33%) from fat
Total energy expended is higher (9 kcal min)
Total fat oxidation is also higher (3 kcal min)
Prolonged low-intensity exercise
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.
Prolonged High intensity exercise
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)
Ingestion of Carbohydrates during endurance activity
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).
Muscle Glycogen
Primary source of carbohydrate during high intensity exercise
Supplies much of the carbohydrate in first hour of exercise
Blood Glucose
From liver glycogenolysis
Primary source of CHO during low intensity exercise
Important during long duration exercise (As muscle glycogen levels decline)
Intramuscular Triglycerides
Primary source of fat during higher intensity exercise
Plasma FFA
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
Sources of Protein During Exercise
Broken down into amino acids
Muscle can metabolize branch chain amino acids and alanine
Liver can convert alanine to glucose
Protein contribution to total energy production
Small (only 2%)
May increase to 5-10% late in prolonged duration exercise
Enzymes that degrade proteins (proteases) are activated in long term exercise.
Lactate as a Fuel Source during exercise
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
Cori Cycle
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
