The Drive with Peter Attia — Iñigo San Millán

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).
  • 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.
  • 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.
  • 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.
  • Altitude training:
    • Improves oxygen carrying capacity.
    • But may reduce glycolytic capacity.

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