4.2.2 Response to exercise

• Muscle contraction


  Requires energy from respiration
• When exercising


  Number of muscle contractions increases
• Greater energy demand


  Muscles need greater supply of oxygen for aerobic respiration
• Human body's reactions to increased oxygen demand


  1. Breathing rate and breath volume increase to increase oxygen absorption and carbon dioxide removal

  2. Heart rate increases

  3. Increased supply of oxygenated blood to muscles
• Exercising vigorously

  Body may not be able to supply sufficient oxygen to muscles
• Anaerobic respiration

  1. Incomplete breakdown of glucose without oxygen

  2. Releases much less energy than aerobic respiration

  3. Results in formation of lactic acid
• Oxygen debt

  Extra oxygen needed to react with lactic acid produced via anaerobic respiration
• After exercising vigorously

  Individual still breathes heavily at increased rate with higher heart rate
• During long periods of vigorous activity

  Muscles become fatigued and stop contracting efficiently due to increased lactic acid
• Investigating effects of exercise on the body


  1. Measure breathing rate and heart rate before and after activity

  2. Plot results on bar chart

  3. Ensure consistent time and full recovery between activities
• Oxygen debt (higher tier only)


  Body can deal with lactic acid by oxidising it to form carbon dioxide and water, or transporting it to the liver to be converted back into glucose