B9.2 The response to exercise

• Your muscles require a lot of energy to carry out their functions. The energy that is transferred during respiration is used to enable your muscles to contract. They contain mitochondria to carry out aerobic respiration and transfer energy when needed. Muscle fibres usually occur in big blocks or groups, which contract to cause movement. They then relax, which allows other muscles to work.
• Your muscles also store glucose as the carbohydrate glycogen. Glycogen can be converted rapidly back to glucose to use during exercise. The glucose is used in aerobic respiration to make your muscles contract
• glucose + oxygen → carbon dioxide + water (energy transferred to the environment)
• C⁶H¹²O⁶ + 6O² → 6CO² + 6H²O (energy transferred to the environment)
• During exercise, the human body responds to the increased demand for energy by:

  • increasing heart rate, breathing rate and breath volume
  • converting glycogen stores into glucose for cellular respiration
  • Increasing flow of oxygenated blood to muscles
• These responses act to increase the rate of supply of glucose and oxygen to the muscles and the rate of removal of carbon dioxide from the muscles