Biology 105
Biology of Exercise
Spring 2003

2/21/03 - Post-class outline

Learning objectives:

How do mechanisms of ATP production differ depending on the type of exercise?

Diagrams.

• Overview of carbohydrate digestion, absorption, and metabolism
• Insulin and glucagon actions
• Anaerobic and aerobic metabolism during sustained exercise
• Glycemic index table (external, from Gatorade Sports Science Institute paper) (choose pdf to print)
• GI exercise
• Table of energy metabolism

Sources of ATP during exercise

• Phosphagen
  • Some ATP is present in the cell and can be used to power muscle contraction
  • Phosphocreatine (P-Cr) can be used to quickly synthesize more ATP.
    • P-Cr + ADP = Cr + ATP
  • The phosphagen system can provide ATP at a very rapid rate, but only for a few seconds (up to 15).
  • It is used at the start of exercise and during very short, intense exercise efforts.
• Anaerobic metabolism
  • glucose (6C) + 2ADP + 2Pi = 2ATP + 2 lactic acid (3C) + heat
  • Can occur in the absence of oxygen
  • Glycolysis is breakdown of glucose to pyruvate
  • Is inefficient in use of glucose (1 glucose yields 2 ATP).
  • Can produce ATP relatively rapidly.
  • Lactic acid is a by-product. Lactic acid has negative effects on cell function.
  • Anaerobic metabolism can produce relatively high power but with low endurance.
• Aerobic metabolism
  • glucose (6C) + oxygen + 36ADP + 36Pi = 36ATP + 6CO2 (1C) + heat + water
    • glycolysis is breakdown of glucose to pyruvate
    • the citric acid cycle (or Krebs cycle or TCA cycle) converts acetyl CoA to high energy intermediates (i.e. NADPH)
    • the electron transport chain converts NADPH into ATP.
  • Efficient in glucose use (36 ATP per glucose)
  • No production of metabolic wastes
  • Slower than anaerobic (more steps than anaerobic)
  • Can produce lower power, but has much higher endurance than anaerobic.
  • Some reactions in aerobic metabolism occur in mitochondria,

Fat metabolism

• Fats can be used only for aerobic metabolism.
• We have enough fat to power aerobic exercise for a very long time.
• Aerobic metabolism of fat can not occur in the absence of carbohydrate metabolism.
• Production of ATP from fat requires slightly more oxygen compared to aerobic metabolism of carbohydrates.
  

How does mechanism of ATP production differ depending on exercise type?

• Time course of energy metabolism during moderate exercise
  • first 10-15 seconds - phosphagen system
  • next 1-2 minutes - anaerobic glycolysis
  • after 1-2 minutes - aerobic metabolism
• Relation to exercise intensity during sustained exerise - see diagram
  • Aerobic metabolism is used at lower intensities.
  • Above the lactic acid threshhold (or anaerobic threshhold), anaerobic metabolism is need to produce higher intensities.
• Fat metabolism vs. carbohydrates for aerobic exercise
  • The amount of fat metabolism increases as duration of exercise increases
  • Fat metabolism is highest during low intensity exercise.
  • Endurance trained athletes metabolize fat earlier and at higher levels than sprinters.