Chapter 69: Exercise Metabolism Flashcards
Two major types of exercise
- Aerobic
- Anaerobic
Aerobic exercise
- Involves prolonged, low intensity exercise (cross-country running or swimming)
Anaerobic exercise
- Requires high intensity work of short duration
Energy for anaerobic exercise
- Derived rapidly by utilizing substrates from within the muscle
Energy for aerobic exercise
- Derived from sources such as fat in adipose tissue or liver glycogen
Three major energy sources for exercise
- Phosphagen system
- Glycogen-lactate system
- Aerobic system
Phosphagen system
- Integrated pools of ATP and creatine phosphate provide maximal muscle power
ATP in the phosphagen system
- Sufficient for maximal muscle power for short bursts (about 4s)
- New ATP must be formed continuously (no ox needed)
- Phosphocreatine reconstitutes a continuous supply of ATP
High-energy phosphate bond of creatine phosphate
- Has more energy than the bond of ATP
- Creatine phosphate can provide enough energy to reform the high-energy bond within a fraction of a second
Creatine phosphate
- High-energy compound
- Stored in muscle cells
- Activated instantly, used to replenish ATP rapidly
Creatine phosphate is made in
- Made in muscle from creatine
- Formed in kidney and liver from amino acids
Creatine phosphate storage
- Not enough is stored or made in the muscle to sustain ATP for more than a few minutes (limited capacity)
Glycogen/lactate system
- Energy production via anaerobic glycolysis (substrate level phosphorylation)
- Stored muscle glycogen converted to g-6-p and utilized for energy
Muscle glycogen becomes lactate (anaerobic) causing
- Metabolic acidosis
- Low pH causes fatigue (PFK-1Iis inhibited)
The flux through the glycolytic pathway can increase by 1000-fold with
- The onset of sudden exercise
Glycogen/lactate system can form ATP molecules
- 2.5x as rapidly as oxidation in mitochondria
- More than ten times less efficient on a molar basis
Aerobic system
- Utilization of pyruvate from glucose or other substrates
- Krebs cycle and oxidative phosphorylation
- Required for prolonged activity
Aerobic system provides
- 95% energy at rest
Preferred substrate for exercising muscle
- Glucose
Sources of glucose for aerobic and anaerobic energy production
- Intramuscular glycogen stores
- Plasma glucose pool
Plasma glucose pool during muscle activity
- Supply, transport and phosphorylation
- Increased muscle GLUT 4 expression with exercise
- Contraction stimulated glucose uptake
Energy substrates for exercise
- Short duration, intense muscle activity = muscle glycogen then blood glucose
Depletion of glycogen reserves during exercise causes
- Switch from carbohydrate oxidation to lipolysis
- Activation of FA oxidation enzymes
- Inhibition of FA synthesis enzymes
Intake of 30-60 gm CHO/hour during strenuous endurance activity
- Delays fatigue by 30-60 minutes
- Maintains plasma glucose levels and high rates of glucose oxidation
- Spares hepatic glycogen reserves
