IGCSE Biology / Breathing and gas exchange
The effect of exercise on breathing
Edexcel International GCSE Biology (4BI1), chapter 3: Breathing and gas exchange, specification point 2.50. Free lesson.
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During exercise, breathing becomes faster and deeper to meet the muscles’ increased demand for oxygen and remove extra carbon dioxide. After exercise, breathing stays raised while the body repays the oxygen debt, and the recovery time can indicate fitness.
How breathing changes during and after exercise
At rest, breathing is steady at about 12 to 15 breaths per minute. When exercise begins, breathing rate rises steeply and reaches a higher level while exercise continues. Breathing also becomes deeper. When exercise stops, breathing rate falls, but takes several minutes to return to normal. The time taken to return to the resting breathing rate is the recovery time. A shorter recovery time usually indicates a higher level of fitness.
Why breathing rate and depth rise
Working muscles need more energy, so their cells respire faster. This increases the demand for oxygen and produces more carbon dioxide. The rise in carbon dioxide is detected, and the brain responds by increasing the rate and depth of breathing. This brings more oxygen into the blood and removes extra carbon dioxide. The change detected is the rise in carbon dioxide, not a fall in oxygen.
Why breathing stays raised after exercise
During exercise, some respiration in the muscles may be anaerobic, which produces lactic acid. After exercise, extra oxygen is still needed to break down the lactic acid. This continued need for oxygen is called the oxygen debt, and breathing stays raised until it is repaid. A fitter person tends to build up less lactic acid and repays the oxygen debt faster. More effective delivery of oxygen to the muscles means more respiration can stay aerobic.
How recovery time shows fitness
Compare how long each person takes to return to their resting breathing rate after doing the same exercise. The person who recovers faster is fitter because less lactic acid built up and the oxygen debt is repaid sooner.