The response to exercise
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of aerobic and anaerobic respiration.
What are the products of aerobic respiration?
Carbon dioxide and water.
What is the word equation for anaerobic respiration in animals?
Glucose → lactic acid.
Why does your body switch to anaerobic respiration during intense exercise?
Because there isn’t enough oxygen available for aerobic respiration.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains the response to exercise, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Response to Exercise
When you exercise, your muscles need more energy for contraction. To meet this demand muscle cells need to do more respiration so require more glucose and oxygen.
Heart Rate and Stroke Volume
-
Heart rate increases – your heart beats faster to pump more blood to the working muscles.
-
Stroke volume increases – each contraction of the heart forces more blood out and around the body, delivering more oxygen and glucose for respiration.
Breathing Rate and Depth
-
Breathing rate increases – more breaths per minute = more oxygen intake and more
release.
-
Depth of breathing increases – deeper breaths bring in more air per breath and exhale more air per breath.
These changes help supply more oxygen to the muscles for aerobic respiration and remove more carbon dioxide.
Anaerobic Respiration During Intense Exercise
If oxygen can’t be delivered fast enough, the muscles switch to anaerobic respiration:
Glucose → Lactic acid
Effects of Anaerobic Respiration
-
Lactic Acid: Builds up in muscles and is toxic at high levels.
-
Muscle Fatigue: Muscles become less efficient, leading to muscle fatigue and reduced performance.
-
Weakened Muscle Contraction: anaerobic releases less energy than aerobic respiration, making muscle contractions weaker.
-
Oxygen Debt: After exercise, extra oxygen is needed to:
-
Break down lactic acid.
-
Repay the "oxygen debt" from anaerobic respiration.
-
That’s why you keep breathing heavily after stopping exercise.
Higher Tier Only
Blood flowing through the muscles will transport lactic acid to the liver where it is converted back into glucose. This requires oxygen.
Oxygen debt is the amount of extra required after exercise to break down the lactic acid in the liver.
Heart rate remains high after exercise to transport extra carbon dioxide to the lungs for exhalation but also, to transport any lactic acid produced during anaerobic respiration to the liver.
No answer provided.
Key Terms
- Heart rate - Number of heart beats per minute.
- Stroke volume - Amount of blood pumped per heartbeat.
- Breathing rate - Number of breaths taken per minute.
- Anaerobic respiration - Energy release from glucose without oxygen.
- Oxygen debt - Extra oxygen needed after exercise to break down lactic acid.
- Muscle fatigue - When muscles work less effectively due to lactic acid build-up.
No answer provided.
Exam Tip
Always link your knowledge of respiration to questions about exercise. Remember, muscles need more energy during exercise for contraction, this energy comes from respiration!
No answer provided.
Practice Question
Explain the changes that happen in the body during and after vigorous exercise. (6 marks)
Examples of marking points
During exercise:
• increased breathing rate / increased breath volume
• to take in more oxygen for aerobic respiration
• and exhale more carbon dioxide
• increased heart rate so increased blood flow to muscles
• to transport oxygen / glucose to respiring cells faster
• and increase rate of carbon dioxide removal
• if insufficient oxygen supplied, anaerobic respiration occurs which produces lactic acid
• and an oxygen debt is created
• lactic acid causes muscles to become fatigued or causes muscles to stop contracting efficiently
After exercise:
• heart rate remains high or heart rate slowly decreases
• continue to breathe rapidly or breathing rate slowly decreases
• to pay back oxygen debt
• oxygen debt is the amount of oxygen needed to break down lactic acid
• lactic acid transported to liver
• and is converted back into glucose
For 5 or 6 marks answers must include need reference to:
• changes during and after exercise
• lactic acid and its removal.
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!