C4 - Cardiovascular System

• The main adaptations that occur to the cardiovascular system through endurance training are concerned with increasing the delivery of oxygen to the working muscles
• If you were to examine the heart of a top endurance athlete, you would find that the size of the walls of the left ventricle are markedly thicker than those of a person who did not perform aerobic exercise training. This adaptation is called cardiac hypertrophy
• Cardiac Hypertrophy is where the size of the heart wall becomes thicker and stronger
• Cardiac Hypertrophy and Cardiac Output:

  • Cardiac Hypertrophy occurs in the same way hat we increase the size of out skeletal muscles - the more we exercise our muscles, the larger or more toned they become
  • The more we exercise our heart through aerobic training, the larger it will become
  • This will then have the effect if increasing the stroke volume, which is the amount of blood that the heart can pump out per beat
• Cardiac Hypertrophy and Cardiac Output:

  • As the heart wall becomes bigger, it can pump more blood per beat
  • As the stroke volume is increased, the heart no longer needs to beat as often to get the same amount of blood around the body
  • This results in a decrease in heart rate which is known as bradycardia
• Bradycardia means a decreased resting heart rate
• Cardiac Hypertrophy and Cardiac Output:

  • As stroke volume increases, cardiac output also increases, so an endurance athlete's heart can pump more blood per minute than a non-trained person's
  • However, resting values of cardiac output do not change
• Sinoatrial Node and Cardiac Cycle:

  • Bradycardia occurs as a result of aerobic training die to a decrease in firing from the sinoatrial node (SAN)
  • The cardiac cycle is controlled by the SAN as this is the pacemaker of the heart
  • The faster the SAN fires, the faster the heart beats and the slower the SAN fires, the slower the heart beats
  • The decrease in firing from the SAN is a result of an increase in vagal tone which is controlled by the parasympathetic nervous system
  • The parasympathetic nervous system is responsible for calming a person down, also known as the rest and digest response
• Vagal tone is the amount if activity form the parasympathetic nervous system which affects the heart rate. An increase in vagal tone decreases heart rate
• Blood Pressure:

  • Aerobic exercise training will reduce a person's resting blood pressure
  • This is because exercise reduces the resistance of blood flow in the arteries
  • However, blood pressure during maximal or sub-maximal exercise will remain unchanged from training
• Blood Composition:

  • The composition of blood will also adapt in response to aerobic exercise training
  • This type of training will increase the amount of haemoglobin in the blood due to an increase in the number of red blood cells which has the effect of further aiding the diffusion rate of oxygen into the blood stream
  • Though haemoglobin content rises, there is also an increase in blood plasma which means that the blood haematocrit (ratio of red blood cell volume to total blood volume) is reduced, which lowers viscosity (thickness) and enables the blood to flow more easily
• Diffusion Rate:

  • The diffusion rate of oxygen into the blood stream increases as a result of aerobic exercise training
  • This occurs due to a variety of factors including:

  1. Capillaries become bigger, allowing more blood to travel through them
  2. New capillaries develop (Capillarisation) which aids in the extraction of oxygen
  3. There is an increase in the oxygen-carrying capacity of the blood due to an increase in haemoglobin concentration