4.2.2 Response to Exercise

During exercise, more energy is needed in order for the muscles to contract. This means respiration has to occur faster, and therefore more oxygen needs to be supplied to cells (and more CO2 removed). This is done by:

• Heart rate increasing
• Breathing rate increasing
• Breath volume increasing

If there is not enough oxygen being supplied (for example when you undertake vigorous exercise) anaerobic respiration takes place instead. As lactic acid is a byproduct of this reaction, it builds up creating an oxygen debt (as oxygen is needed to break lactic acid down). 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. This results in the muscles tiring and not contracting properly.

Blood flowing through the muscles transports the lactic acid to the liver where it is converted back to glucose.