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Acute Responses to Exercise

Cardiopulmonary Aspects

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Responses to Exercise

Exercise places demands on the physiological systems in the human body resulting in multiple responses. These answers are based on[1]:

  • Type or mode of exercise
  • Intensity of exercise
  • Duration of exercise
  • Frequency of exercise
  • Environmental conditions[2]
  • Emotional influences[3]
Cardiovascular System
  • Components[4]:
    • Circulatory system
    • Pulmonary system
  • Function[4]:
    • Transfer and exchange of respiratory gases (oxygen and carbon dioxide) .
    • Transportation and exchange of nutrients and wastes
    • Hormone and chemical messengers
    • Thermoregulation of body temperature .
    • Regulation of fluid balance
    • Regulation of blood pressure
    • Maintenance of pH balance
    • Prevention of blood loss by hemostatic techniques
    • Prevention of infection by white blood cells and lymphoid tissue

Read more: Cardiovascular System

Heart Rate

  • Increases linearly with workload and oxygen consumption (VO2) during dynamic exercise
  • Heart rate (HR) response may be influenced by the following factors [5]:
    • age
    • body position
    • fitness
    • type of activity
    • medication
    • environmental conditions
    • blood volume
Maximal Heart Rate
  • Maximum heart rate (HRmax) is achieved after exerting yourself to the point of mental fatigue. [6] It is the highest heart rate a person can achieve when they are exerting themselves to the point of exhaustion.
  • HRmax is NOT trainable
  • HRmax remains constant daily and decreases slightly each year
  • HRmax can be estimated:
    • HRmax = 220 – age (this is the most common and widely used formula)
    • HRmax = 208 – (o.7 x age in years) – This is a more precise formula adjusted for people over 40
    • HRmax = 211 – (o.64 x age) – a more precise formula adjusted for the general active population
  • A female’s maximum heart rate is approximately 5 – 10 beats per minute
  • HRmax decreases with age through adrenergic receptor desensitization
  • Assessment of HRmax:
    • Laboratory setting
      • Graded exercise test
    • Field test
      • Running and cycling protocols
  • Used in performance prediction
  • Health status
Steady-State Heart Rate
  • Optimal heart rate to meet cycling demands at a given submaximal workload/intensity
  • The lower the steady state heart rate for a given workload/intensity
    • Efficiency
      • Enhanced contractility
      • Increased stroke volume
  • Functional capacity prediction based on steady-state heart rate

Maximal Oxygen Consumption (VO2 max)

  • Gold standard assessment
  • Product of maximal cardiac output (Q) and arteriovenous difference (a – vO2)
  • The body’s maximum ability to use oxygen to produce energy
  • Differences in maximal oxygen uptake in healthy people
    • Due to differences in maximum stroke volume (SVmax)
    • Some due to (a – vO2)max

VO2max = HRmax x SVmax x (a-vO2)max

Stroke Volume
  • End-diastolic volume (EDV) depends on heart rate filling pressure and ventricular compliance
  • End systolic volume (ESC) depends on afterload and contraction force
  • Resting stroke volume (SV): 60 – 100 mL/beat
  • Maximal stroke volume: 100 – 120ml/beat
  • Maximize at about 50% of your best effort


Regulation of Stroke Volume
  • End-diastolic volume (EDV)
    • End-diastolic ventricular blood volume (preload)
  • Average aortic blood pressure
    • The pressure with which the heart must pump to expel blood (afterload)
    • Increased afterload = decreased stroke volume (usually in sick people rather than in healthy exercisers)
  • Strength of the ventricular contraction
    • “Contractility”
End Diastolic Volume
  • Frank Starling mechanism
    • Greater preload results in ventricular stretch and more forceful contraction
  • Affected by:
    • Vasoconstriction
    • Skeletal muscle pump
    • Respiratory pump
Cardiac Output
  • Cardiac output(Q) = HR X SV
  • Rest: 5 L/min
  • Maximal: 20 L/min or more
  • Up to about 50% of best effort HR and SV contribute to Q increase
Ejection Fraction
  • SV/EDV X 100
  • Normal 65% (55% – 70%)

Heart rate stroke volume and cardiac output – rest and activity

  • Standing increases venous blood flow to the most dependent parts of the body
  • This redistribution of blood results in less blood in the chest cavity returning to the heart. Through the Frank Starling mechanism, this results in a reduction in stroke volume (30% to 40% reduction)
  • This rises again when returning to the supine position in response to increased venous return

Heart Rate Stroke Volume and Cardiac Output – Resting and Maximum (Peak)


Blood Pressure

  • Systolic blood pressure (SBP)
    • Linear increase, 8-12 mmHG/MET
  • Diastolic blood pressure (DBP)
    • slight decrease or increase or no change
Arteriovenous Oxygen Difference (a-vO2)
  • the amount of oxygen extracted from the blood as it flows through the body
  • Calculated as the difference between arterial and venous oxygen levels
  • Increases with movement speed as more oxygen is drawn from the blood
    • Rest (20ml O2/100ml – 15ml O2/100ml) = 5ml O2/100ml
    • Maximum exercise volume: 20 ml O2/100ml – 5 mlO2 ml/100ml = 15 ml O2/100 ml
    • Utilisation coefficient: 25 – 75%
Pulmonary Ventilation (Ve)
  • Ve = RR x TV
  • TV = volume of air inhaled in one breath
  • Rest: 6L/min
  • Maximal: 15 – 25 fold increase
  • Mild to moderate exercise
    • Ve increases mainly due to increased TV
  • Intense exercise
    • RR is important…proportional to exercise intensity
Blood Flow
  • Rest: 15 – 25% of Q to skeletal muscle
  • Exercise: 85 -90% of Q to skeletal muscle
  • 5-fold increase in flow to the heart
  • Decreased cutaneous renal hepatic and splanchnic blood flow during exercise
  • Only minor changes in blood flow to the brain
Transition from rest to exercise and exercise to recovery
  • Intensity-dependent adaptations to HR SV Q SBP RR Ve and VO2
  • Plateaus during submaximal (below lactate threshold) exercise
  • Recovery depends on:
    • Duration and intensity of exercise
    • Training state of the individual
Prolonged Exercise
  • Cardiac output is maintained
    • Gradual decrease in stroke volume
    • Gradual increase in heart rate
  • Cardiovascular drift
    • Due to dehydration and increased skin blood flow (increased body temperature) .
    • Due to decreased venous return

Acute Physiologic Exercise Responses

  • Exercise Pressor Response
    • Invoked by muscle contraction
      • Nerve receptors are stimulated by nerve changes or metabolic byproducts – afferent signal transmission to the CNS
    • Sympathetic nervous system phenomena
      • Generalized vasoconstriction in nonfunctioning skeletal muscle
      • Increased myocardial contractility
      • Increased HR
      • Increased SBP
      • Increased and redistribution of Q
      • Response = exercise intensity
  • One of the major challenges to exercise-induced homeostasis is the increased tissue oxygen demand
  • During strenuous exercise, oxygen demand can increase 15 to 25 times
  • Two major adjustments of blood flow are:
    • Increased cardiac output
    • Redistribution of blood flow
  • Depends on:
    • Type, intensity and duration of exercise
    • Environmental conditions
    • Emotional influence
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  1.  Ansdell P, Thomas K, Hicks KM, Hunter SK, Howatson G, Goodall S. Physiological sex differences affect the integrative response to exercise: acute and chronic implications. Experimental Physiology. 2020 Dec;105(12):2007-21.
  2.  Travers G, Kippelen P, Trangmar SJ, González-Alonso J. Physiological Function during Exercise and Environmental Stress in Humans—An Integrative View of Body Systems and Homeostasis. Cells. 2022 Jan 24;11(3):383.
  3.  Bernstein EE, Curtiss JE, Wu GW, Barreira PJ, McNally RJ. Exercise and emotion dynamics: An experience sampling study. Emotion. 2019 Jun;19(4):637.
  4. ↑ Jump up to:4.0 4.1 Smith DL, Fernhall B. Advanced cardiovascular exercise physiology. Human Kinetics; 2022 Feb 27.
  5.  Ludwig M, Hoffmann K, Endler S, Asteroth A, Wiemeyer J. Measurement, prediction, and control of individual heart rate responses to exercise—Basics and options for wearable devices. Frontiers in physiology. 2018 Jun 25;9:778.
  6.  Berglund IJ, Sørås SE, Relling BE, Lundgren KM, Kiel IA, Moholdt T. The relationship between maximum heart rate in a cardiorespiratory fitness test and in a maximum heart rate test. Journal of science and medicine in sport. 2019 May 1;22(5):607-10.

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