Acute Responses to Exercise

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Cardiopulmonary Aspects[edit | edit source]

Back to Basics[edit | edit source]

Responses to Exercise[edit | edit source]

Exercise imposes demands on physiological systems in the human body that leads to several responses. These responses are dependent on[1]:

  • Type or mode of exercise
  • Intensity of exercise
  • Duration of exercise
  • Frequency of exercise
  • Environmental conditions[2]
  • Emotional influences[3]

Cardiovascular System[edit | edit source]

  • Components[4]:
    • Circulatory system
    • Pulmonary system
  • Function[4]:
    • Transport and exchange of respiratory gases (oxygen and carbon dioxide)
    • Transport and exchange of nutrients and waste products
    • Transport of hormones and chemical messengers
    • Regulation of body temperature (thermoregulation)
    • Regulation of fluid balance
    • Regulation of blood pressure
    • Maintenance of pH balance
    • Prevention of blood loss through haemostatic mechanisms
    • Infection prevention through white blood cells and lymphatic tissue

Read more: Cardiovascular System

Heart Rate[edit | edit source]

  • Linear increase with workload and oxygen consumption (VO2)during dynamic exercise
  • Heart rate (HR) response may be influenced by[5]:
    • age
    • body position
    • fitness
    • type of activity
    • medication
    • environmental conditions
    • blood volume
Maximal Heart Rate[edit | edit source]
  • Maximum heart rate (HRmax) is achieved after all-out exertion to volitional fatigue.[6] It is the highest heart rate value one can achieve in an all-out effort to the point of exhaustion.
  • HRmax is NOT trainable
  • HRmax remains constant day to day and decreases slightly from year to year
  • HRmax can be estimated:
    • HRmax = 220 - age in years (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 older than 40 years
    • HRmax = 211 - (o.64 x age in years) - even more precise formula, adjusted for generally active people
  • In women HRmax is about 5 - 10 beats per minute greater
  • HRmax decreases with age through adrenergic receptor desensitisation
  • Assessment of HRmax:
    • Laboratory setting
      • Graded exercise test
    • Field test
      • Running and cycling protocols
  • Used in performance prediction
  • Health status
Steady-State Heart Rate[edit | edit source]
  • Optimal heart rate for meeting circulatory demands at a given sub-maximal workload/intensity
  • The lower the steady-state heart rate at a given workload/intensity
    • Efficiency
      • Enhanced contractility
      • Increased stroke volume
  • Predictions of functional capacity based on steady-state heart rate

Maximal Oxygen Consumption (VO2 max)[edit | edit source]

  • Gold standard assessment
  • Product of maximal cardiac output (Q) and arteriovenous difference (a - vO2)
  • Maximal ability of the body to consume oxygen for production of energy
  • Differences in VO2max in healthy individuals
    • Due to differences in maximum Stroke Volume (SVmax)
    • Some due to (a - vO2)max

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

Stroke Volume[edit | edit source]

  • End diastolic volume (EDV) is dependent on heart rate filling pressure and ventricular compliance
  • End systolic volume (ESC) is dependent on afterload and contractility
  • Stroke volume (SV) at rest: 60 - 100 ml/beat
  • Maximal stroke volume: 100 - 120ml/beat
  • Reaches a maximal value at approximately 50% of maximal effort


Regulation of Stroke Volume[edit | edit source]
  • End-diastolic volume (EDV)
    • Volume of blood in the ventricles at the end of diastole ("preload")
  • Average aortic blood pressure
    • Pressure that heart must pump against to eject blood ("afterload")
    • Increased afterload = decreased stroke volume (usually in ill individuals and not in healthy athletic populations)
  • Strength of the ventricular contraction
    • "Contractility"
End Diastolic Volume[edit | edit source]
  • Frank Starling mechanism
    • Greater preload results in stretch of ventricles and in a more forceful contraction
  • Affected by:
    • Vasoconstriction
    • Skeletal muscle pump
    • Respiratory pump

Cardiac Output[edit | edit source]

  • Cardiac output(Q) = HR X SV
  • Rest: 5 L/min
  • Maximal: 20 L/min or more
  • Up to approximately 50% of maximum effort, HR and SV both contribute to an increase in Q
Ejection Fraction[edit | edit source]
  • SV/EDV X 100
  • Normal 65% (55% - 70%)

Heart Rate, Stroke Volume, and Cardiac Output - Rest and Activity[edit | edit source]

  • Standing up increases the venous pooling of blood in the most dependent parts of the body
  • This redistribution of blood causes a reduction in the intrathoracic blood volume returning to the heart. Through the Frank Starling mechanism, this causes a reduction in the stroke volume (by 30% to 40%)
  • This rises again when going back to a supine position, in response to increased venous return

Heart Rate, Stroke Volume, and Cardiac Output - Rest and Maximum (Peak)[edit | edit source]


Blood Pressure[edit | edit source]

  • Systolic blood pressure (SBP)
    • Linear increase, 8-12 mmHG/MET
  • Diastolic blood pressure (DBP)
    • Slight decreases or increases or no change

Arteriovenous Oxygen Difference (a-vO2)[edit | edit source]

  • Amount of oxygen extracted from the blood as it travels through the body
  • Calculated as the difference between the oxygen content of arterial blood and venous blood
  • Increases with increasing rates of exercise as more oxygen is taken from blood
    • Rest (20ml O2/100ml - 15ml O2/100ml) = 5ml O2/100ml
    • Maximal exercise: 20 ml O2/100ml - 5 mlO2 ml/100ml = 15 ml O2/100 ml
    • Utilisation coefficient: 25 - 75%

Pulmonary Ventilation (Ve)[edit | edit source]

  • Ve = RR x TV
  • TV = volume of air breathed in a single breath
  • Rest: 6L/min
  • Maximal: 15 - 25 fold increase
  • Mild to moderate exercise
    • Ve is increased primarily due to an increase in TV
  • Intense exercise
    • RR is important...proportional to intensity of exercise

Blood Flow[edit | edit source]

  • Rest: 15 - 25% of Q to skeletal muscle
  • Exercise: 85 -90% of Q to skeletal muscle
  • 5-fold increase in flow to the heart
  • Decrease in skin, renal, hepatic, and splanchnic blood flow during exercise
  • Only small changes of blood flow to the brain

Transition from Rest to Exercise and Exercise to Recovery[edit | edit source]

  • Intensity dependent adaptations to HR, SV, Q, SBP, RR, Ve and VO2
  • Plateau in submaximal (below lactate threshold) exercise
  • Recovery depends on:
    • Duration and intensity of exercise
    • Training state of the individual

Prolonged Exercise[edit | edit source]

  • Cardiac output is maintained
    • Gradual decrease in stroke volume
    • Gradual increase in heart rate
  • Cardiovascular drift
    • Due to dehydration and increased skin blood flow (rising body temperature)
    • Due to decreased venous return

Acute Physiologic Exercise Responses[edit | edit source]

  • Exercise Pressor Response
    • Invoked by muscle contraction
      • Muscle receptors are stimulated by muscular distortion or metabolic byproducts - afferent signal transmission to CNS
    • Sympathetic nervous system phenomena
      • Generalised vasoconstriction in nonactive skeletal muscle
      • Increased myocardial contractility
      • Increased HR
      • Increased SBP
      • Increased and redistribution of Q
      • Response = exercise intensity
  • One major challenge to homeostasis posed by exercise is the increased muscular demand for oxygen
  • During heavy exercise, oxygen demands may be higher by 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

Resources[edit | edit source]

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  1. numbered list
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References[edit | edit source]

  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. 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.