This is the process that releases energy from food, converting glucose into energy.

There are 2 kinds of respiration:

Aerobic respiration -with oxygen (O₂)

During aerobic activity, your heart and lungs supply the muscles with O₂

Glucose + O₂ > CO₂+ H₂O + energy

You breath out the CO₂ through your lungs, and lose water through sweat, urine or in the air.

As long as your muscles are supplied with enough O₂, you can take part in aerobic exercise, so this is used for long periods of exercise.

e.g. Marathon runners

Anaerobic respiration -without oxygen

Muscles are not supplied with enough O₂ during this

Glucose + no O₂ > lactic acid + energy

Lactic acid builds up if there is a shortage of O₂ (O₂ debt).

This is a mild poison, which makes the muscles feel tired, so is used over short, strenuous activities.

e.g. Sprinters