1.11 - Oxygen Debt

Oxygen debt and recovery

• During very vigorous exercise, the muscles can't get enough oxygen to meet their energy demand by aerobic respiration alone, so they also respire anaerobically.
• Anaerobic respiration only partly breaks down glucose and releases far less energy. It produces lactic acid, which builds up in the muscles and in the blood.
• When exercise stops, this build-up has to be cleared - and clearing it needs oxygen.

Oxygen debt

• The oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.
• To repay the debt after stopping:
  • Breathing rate and depth of breathing stay high for a while, taking in extra oxygen. The deep breathing supplies the oxygen.
  • Heart rate also stays high, keeping the blood moving so it carries the lactic acid away from the muscles.

Clearing the lactic acid

• The blood transports the lactic acid to the liver.
• In the liver, the lactic acid is broken down using oxygen (aerobic respiration) and converted back into glucose.
• Pulse and breathing rate stay raised until the lactic acid and the extra carbon dioxide have been cleared, at which point they return to normal.