What is oxygen debt? When you have a short intense burst of exercise such as sprinting you generate energy for this anaerobically or without oxygen. When you stop exercising you are still breathing heavily. This is your body taking in extra oxygen to 'repay' the debt. Well, that is the simple solution but there is a little more to it if you want to look a bit deeper.
True, your body has worked anaerobically and will have produced energy without some of the oxygen it would normally have used performing low intensity exercise such as slow steady running. The difference between the oxygen the body required and what it actually managed to take in during the sudden sprint is called oxygen deficit.
When you stop sprinting and start to recover you will actually need more oxygen to recover than your body would have liked to use had enough been available. This is called Excess Post Exercise Oxygen Consumption.
So why does it take more oxygen to recover then?
- You needed to replace the oxygen the body needed but couldn't get (oxygen deficit).
- Breathing rate and heart rate are elevated (to remove CO2) and this needs more oxygen.
- Body temperature and metabolic rate is increased and this needs more oxygen.
- Adrenaline and Noradrenaline are increased which increases oxygen consumption.
So after exercise there are other factors causing an increase in oxygen needs as well as repaying the lack of oxygen during exercise.
The chart below is often seen and shows how the amount of oxygen used by the body changes over time. At the beginning the body works anaerobically leaving an oxygen deficit. Over time the oxygen consumption levels out to a steady state. After exercise the oxygen is pain back (oxygen debt). Notice the area of oxygen debt is greater than the area of oxygen deficit for the reasons stated above.
What has Lactic Acid got to do with it?
Lactic acid is a by product of exercising without using oxygen (anaerobically). It is essential this is removed but it is not necessarily a waste product. It is recycled into other useful chemicals:
- During prolonged intensive exercise (e.g. 800m race) the heart may get half its energy from lactic acid. It is converted back to pyruvic acid and used as energy by the heart and other muscles.
- It is thought that 70% of lactic acid produced is oxidized, 20% is converted to glucose (energy) in the liver.
- 10% is converted to protein.
How long does it take to remove lactic acid?
- About 1 hour if cooling down with gentle exercise.
- It can take 2 hours or more if you don't warm down with gentle exercise.