On: Mitochondria, exercise, and metabolic health
Episode: 85
Date: December 2019
Background: Researcher in sports medicine and performance, diabetes, cancer and critical care medicine.
Key Subjects:
- Breakdown into six different metabolic training zones based on:
- Type of muscle fiber recruited: slow or fast twitch.
- Type of cellular fuel use: fatty acids, or glucose.
- Energy system: existing ATP stores (anaerobic), glycolysis (anaerobic), mitochondrial respiration (aerobic).
- See “Exercise – Energy Systems and Exercise Zones“.
- A lot of exercise is low intensity and involves the aerobic burning of fat.
- Known as zone 2 (when you can still carry on a conversation).
- At training intensity increases, we start using glucose as fuel and use less fat.
- Zone 3: oxidize both fats and glucose in mitochondria (aerobic).
- Zone 4: oxidize glucose in mitochondria (aerobic).
- Zone 5: glycolysis of glucose in cytosol (anaerobic).
- At higher intensity, use more glucose, create more lactate.
- Lactate is produced by Type II fibers during anaerobic exercise (glycolysis).
- Glucose -> pyruvate -> lactate (similar to fermentation pathway).
- Lactate is produced by Type II fibers during anaerobic exercise (glycolysis).
- Old thesis: lactate is a toxic metabolic by-product and makes you tired.
- During anaerobic exercise, excess lactate goes into the bloodstream.
- Goes back to the liver where it is cleared.
- Causes fatigue and muscle pain.
- Complementary new thesis: lactate shuttle.
- Lactate is formed not only under anaerobic conditions, but also in the presence of oxygen.
- Lactate is not only cleared by going into the blood stream, it is also transported into mitochondria for fuel.
- Done by Type I fibers.
- The oxidation of lactate in the mitochondria can be a major energy source.
- Elite athletes: high ability to burn fat and clear lactate.
- Indicates strong mitochondrial health.
- Elite athletes have more and larger mitochondria.
- High ability to burn fat = don’t rely on glucose as fuel too early = don’t produce a lot of lactate.
- High ability to clear lactate = mitochondria can use it as fuel = blood glucose levels don’t rise too early.
- Indicates strong mitochondrial health.
- Diabetes is the opposite: not good at burning fat or clearing lactate.
- Rely more on glucose as fuel, burn little fat, produce a lot of lactate, blood lactate levels rise quickly.
- Heart rate training.
- May make sense.
- Heart rate is a physiologic parameter and responds to physiologic and metabolic stress.
- Heart rate increases in line with lactate increases.
- Exercise and restricting carbs.
- May not make sense.
- Especially in situations requiring glycolysis, ie where you need glucose as a fuel.
- Tends to lead to lower power output, lower lactate, lower heart rate.
- There may be longer-term metabolic adaptation, but most athletes can’t wait for that to happen.
- Exercise and insulin sensitivity.
- Exercise increases insulin sensitivity.
- More efficient uptake of glucose by the muscles.
- Exercise also increases non-insulin dependent glucose uptake.
- Muscle contraction has similar impact on glucose uptake as insulin.
- Exercise increases insulin sensitivity.
- Regular low intensity Zone 2 training improves metabolic flexibility.
- Use and build Type 1 fibers.
- Better mitochondria (Type I has highest density of mitochondria).
- Better fuel partitioning (burn more fat, preserve glycogen, produce less lactate).
- Clear more lactate (done by Type I fibers).
- 2x a week for about an hour.
- Use and build Type 1 fibers.
- Altitude training:
- Improves oxygen carrying capacity.
- But may reduce glycolytic capacity.