B3 Training and the Cardiovascular System

B.3.1  Define heart rate, stroke volume, cardiac output and venous return

Heart rate:  Number of contractions of the heart per minute

Stroke volume:  Volume of blood pumped out with each contraction of the heart

Cardiac output:  Volume of blood pumped out by the heart per minute

Venous return:  Volume of blood returning to the heart via the veins per minute

B.3.2  Explain the changes in cardiac output and venous return during exercise

  • The cardiac output is a product of both heart rate and stroke volume (CO = HR × SV)
  • Exercise increases the production of carbon dioxide by respiring cells, which lowers the pH of the blood
  • Detection of lowered blood pH causes impulses to be sent by the brain to the pacemaker, which increases cardiac output by:
    • Increasing heart rate (more contractions per minute)
    • Increasing stroke volume (due to greater contractile force of the cardiac muscle)
  • Contraction of muscles used during exercise squeezes blood in adjacent veins, increasing venous return (which increases stroke volume)

B.3.3  Compare the distribution of blood flow at rest and during exercise

  • Blood flow to the brain is largely unchanged during exercise
  • Blood flow to the heart wall, skeletal muscles and skin is increased
  • Blood flow to the kidneys, stomach, intestines and other abdominal organs is decreased

Distribution of Blood Flow at Rest and During Heavy Exercise

Blood flow during exercise

B.3.4  Explain the effects of training on heart rate and stroke volume, both at rest and during exercise

When training, the heart beats more frequently (ñ heart rate) and with greater strength (ñ stroke volume) in order to supply muscles with oxygen 

  • Training consequently causes the enlargement and strengthening of cardiac muscle (particularly in the left ventricle) due to the increased level of work
  • This increases the stroke volume of the heart at rest (due to stronger heart muscle), resulting in an increase in cardiac output overall
  • The increase in stroke volume reduces the number of beats required to maintain cardiac output, so heart rate overall decreases at rest

As a consequence of these changes, when exercising:

  • Stroke volume (and therefore cardiac output) increases more rapidly
  • Heart rate increases more gradually
  • Recovery to normal cardiac output after exercise is faster
  • Resting pulse rate will be lower

B.3.5  Evaluate the risks and benefits of using EPO (erythropoietin) and blood transfusions to improve performance in sports

  • Erythropoietin (EPO) is a glycoprotein hormone produced in the kidneys that is responsible for red blood cell production (erythropoiesis)
  • Blood transfusions involve the intravenous injection of blood components (e.g. red blood cells) into the body


  • Both increase levels of red blood cells (EPO increases production, blood transfusion increases supply)
  • More red blood cells means more haemoglobin, allowing for greater levels of oxygen transport to respiring muscles
  • Improves performance and endurance compared to athletes that do not use these methods


  • Too many red blood cells can produce damage in capillaries by increasing blood clotting, leading to heart failure and strokes
  • Risk of disease transmission or possible rejection when undergoing blood transfusions
  • Increased blood viscosity (due to higher cell count) increases blood pressure
  • Limited information on long-term health effects (more relevant to EPO)
  • Unfair advantage to athletes can result in banning or disqualification from competitions