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
Metabolic activity during exercise
- Increased glucose delivery to muscle
- Lactate from anaerobic exercise is removed (will inhibit PFK-1
- Note also FA and ketone body use by muscle
The increased uptake of glucose from the blood by exercising muscle may benefit the diabetic patient
- Even if insulin is not working
- Recall how obesity can lead to type II DM
Major fuel for prolonged, low-intensity activity
- Fat
- Majority of stored energy in the body (concentrated)
- TAGs broken down to free FAs and glycerol
Fatty acids travel to muscle cells and can be converted to
- Acetyl-SCoA in the mitochondria
- Generates lots of ATP (2x as much as CHO and protein metabolism)
Marathon running fat consumption
- 50:50 FA:CHO
Elevated hormones during exercise
- Glucagon
- Cortisol
- Adrenaline
- Noradrenaline
- Growth hormone
Depressed hormones during exercise
- Insulin (hormone-sensitive lipase will be on)
The conversion of liver glycogen to glucose
- Promoted during exercise
- Raises plasma glucose levels
- Glucose is available for uptake by the exercising muscle cells
No glucose uptake by fat during exercise because
- Requires insulin (depressed during exercise)
- Recall enzymes of glycogenolysis and glycogenesis
Carbohydrate loading
- Consumption of carbs post-workout to replenish depleted stores (oxidation of carbs is an energy source)
Benefits of carbohydrate loading for exercise
- Typically better for events lasting longer than 90 minutes
- Maximizes muscle glycogen stores and delays onset of fatigue
- Tapering of exercise while increasing CHO intake
- Increases stores by 50-85%
Most effective exercise for burning calories
- Combination of resistance exercise and aerobic exercise
Maintenance of lean muscle tissue is a result of
- Increased mitochondrial content
Enhanced insulin action of regular exercise seen mostly in
- Moderate intensity exercise (brisk walking)
- Aiming for 5-10% weight loss is the cornerstone of management of type II DM
