D impact of physical activity on SV, HR and CO

• stroke volume is the volume of blood pumped out by heart ventricles in each contraction
• average resting stroke volume is 70ml
• what 3 factors does stroke volume depend on?

  1. venous return
  2. elasticity of cardiac fibres - amount of stretch of cardiac tissue during diastole phase. more cardiac fibres means greater force of contraction which results in greater ejection fraction
  3. contractility of cardiac tissue - greater contractility of cardiac tissue results in greater force of contraction
• heart rate

  number of times heart beats per minute. average = 72
• cardiac output is volume of blood pumped out by heart ventricles per minute
• Q = SV x HR
• what happens with heart rate during exercise?

  • increases in direct proportion to exercise intensity
  • reaches maximum. max HR = 220 - age
• what happens to HR during maximal exercise?

  1. anticipatory rise due to release of adrenaline causes SAN to increase HR
  2. sharp rise in HR due to anaerobic work
  3. HR continues to rise
  4. rapid decline in HR when exercise stops
  5. HR remains elevated to rid body of waste products
• what happens to HR during sub-maximal exercise?

  1. anticipatory rise due to release of adrenaline which causes SAN to increase HR
  2. sharp rise in HR due to anaerobic work
  3. athlete meets oxygen demand with oxygen supply causing a steady state
  4. rapid decline in HR when exercise stops
  5. HR remains elevated to rid body of waste products
• what happens to cardiac output during exercise?

  • large increase in cardiac output due to increase in HR and SV
  • plateaus when maximum exercise intensity reached
• what happens to cardiac output for a trained and untrained performer?

  • stays same for both performers at rest
  • during exercise, trained performer has greater cardiac output
• what happens to stroke volume during exercise?

  • increases as exercise intensity increases
  • after 40-60% of maximum effort, SV plateaus. this is due to shorter diastole phase