Exercise physiology

• Cardiovascular system

  Serves numerous important functions within the human body that supports all other physiological systems including:

  • Delivery of oxygen and energy substrates
  • Removal of CO2 and other metabolic waste products
  • Transport of hormones
  • Thermoregulation and control of body fluid balance
  • Maintenance of acid-based balance (to control pH)
  • Regulation of immune function
• Cardiovascular system

  • Essential for health, disease and performance

  High adaptive to stress

  Vulnerable to disease
• Cardiovascular responses to acute exercise

  In response to exercise, there are several interrelated changes that occur with the main aim of supplying greater volumes of oxygenated blood to the working muscles

  Involves a coordinated response of both the central and peripheral circulation in order to ensure enough blood supply for metabolism
• Heart rate

  Number of beats within one minute
• Systole

  The phase of heart contractility
• Diastole

  The phase of heart relaxation
• Stroke volume

  The volume of blood pumped from the left ventricle per beat
• Cardiac output

  Volume of blood pumped through the circulatory system per minute
• 1. vO2 difference

  Difference in the O2 saturation between arterial and the venous blood
• VO2 and VO2max

  Volume of oxygen that is used by your body to convert the energy
• Heart rate

  • Simple but informative measure often used in the physiological assessment of patients/athletes as an indirect measure of cardiovascular stress and strain

  Can be used to inform the relative intensity of exercise
• Key measures of heart rate

  • Resting heart rate

  Maximum heart rate

  Heart rate reserve

  Heart rate variability

  Heart rate recovery
• Increase in exercise intensity

  Directly proportional increase in heart rate
• If we continue to increase the intensity beyond 100%, would HR continue to rise?
• To accurately determine the HR response to a given intensity, we must achieve steady-state
• Steady-state is the optimal HR for meeting the circulatory demands of work and takes approximately 3 minutes
• An example of changes in HR indices

  • Resting HR and post-ex HR provides a measure of the rhythmic fluctuation due to a continuous change in sympathetic and parasympathic rhythm

  HRR - the rate of reduction in HR once exercise has ended (i.e. no. beats in 60 seconds)
• Stroke volume

  The volume of blood pumped from the heart (left ventricle) per beat
• Factors influencing stroke volume

  • Venous return

  Ventricular distensibility

  Ventricular contractility

  Aortic or pulmonary pressure

  End diastolic volume (preload)

  Afterload (systole)
• Think of a disease that might affect one or more of these factors of stroke volume
• Stroke volume response to exercise

  Increases rapidly up to 40-60% of VO2max

  After this, stroke volume rises but at a much slower rate - it reaches a limit of the four factors mentioned
• Cardiac output response to exercise

  ≤ 50% VO2max = increase in stroke volume and increase in heart rate

  ≥ 50% VO2max = no change in stroke volume and increase in heart rate
• Stroke volume plateaus at approximately 50% of VO2max
• Contrasting evidence suggests that stroke volume can continue to increase at intensities > 50% VO2max
• Factors affecting stroke volume response to exercise

  • Activity type

  Age

  Fitness levels

  Sex

  Hydration status
• At 70 b·min-1 filling time is ~0.55 s but at 195 b·min-1 this is reduced to 0.12

  Greater filling = greater stretch = greater ejection fraction (Frank-Starling mechanism)
• Increase in preload

  Increases stroke volume
• Decrease in afterload (total peripheral resistance)


  Increases stroke volume
• Cardiac output

  Q = SV x HR

  Rest = ~ 5 L

  Max = 20 to 40 L
• At max intensity, cardiac output reaches a plateau
• Fick principle

  VO2 = Q x (a-v)O2 difference
• 1. vO2 difference

  Resting metabolism consumes about 5 mL of oxygen from the 20 mL oxygen in each decilitre of arterial blood (50 mL ⋅ L−1) that passes through the tissue capillaries

  This changes to 4 mL ⋅ dL−1 during maximum exertion
• Factors affecting resting cardiovascular values

  • Sex

  Age

  Exercise & physical activity status

  Body position

  Activity type

  Muscle contraction(s)

  Various clinical conditions

  Activity level before assessment

  Body composition

  Genetics / Epigenetics

  Activity intensity / volume
• Effect of bed rest on cardiovascular function
• Effect of age on VO2max

  Children: Absolute values similar up to 12yrs after which males and females differ

  Relative values: boys remain constant (52 ml·kg-1·min-1); girls decrease to about 40 ml·kg-1·min-1 at 16 yrs

  Decrease after 25 yrs at about 1% per year

  Evident even with training

  Physical activity levels have greater influence on VO2max than chronological age
• Effect of sex on VO2max

  Females < males by 15 - 30%

  Magnitude dependent upon how VO2max is expressed (absolute vs relative)

  Differences attributed to body fat levels, haemoglobin concentration, and activity levels
• Exercise modality and VO2max

  Treadmill > Cycle

  Significant difference