Heart Rate & Exercise (Edexcel IGCSE Biology: Double Science)

Control of the heart rate

• A heart rate is measured by counting the number of times a heart beats in a minute (bpm)
  • Factors such as exercise or levels of adrenaline, will affect the rate of 
• The natural resting heart rate is controlled by a group of cells located in the right atrium called the pacemaker
  • The role of the pacemaker is to coordinate the contraction of the heart muscle and regulate the heart rate
  • Pacemaker cells send out electrical impulses which initiate a contraction in the cardiac muscle

Exercise and heart rate

• The heart pumps blood to respiring cells to supply oxygen and glucose and remove respiratory waste
• During exercise, muscle cells respire faster to increase energy supply
  • Respiration is aerobic during moderate exercise and anaerobic during intense exercise
• Increased respiration raises the need for oxygen, glucose, and waste removal
• The nervous system responds by:
  • Increasing heart rate to deliver oxygen and glucose more frequently
  • Increasing the volume of blood pumped to supply larger amounts of oxygen and glucose
• At the end of a period of exercise, the heart rate may remain high for a period of time as oxygen is required in the muscles to break down the lactic acid from anaerobic respiration

• Production of the hormone adrenaline also increases heart rate as part of a 'fight or flight' response