Physiology of Exercise

PHYSIOLOGY OF EXERCISE
WHO CLASSIFICATION OF EXERCISE
Grade Level Relative load index Metabolic energy expenditure test (METS) heart rate Heart rate
I Mild < 25% of VO2 max < 3 METS < 100/min
II Moderate 25-50% of VO2 max 3-4.5 METS 100-125/min
III Heavy 51-75% of VO2 max 4.6-7 METS 126-150/min
IV Very Heavy (Severe) >75% of VO2 max > 7 METS >150/min
  • Cerebral blood flow remains constant during moderate exercise even in the face of a small rise in systemic blood pressure, however in heavy exercise hypocapnia secondary to hyperventillatory response will cause local cerebral vasoconstriction.
CHANGES IN THE BLOOD AND LYMPHATIC FLOW DURING EXERCISE:
  • During Exercise blood is shunted from regions that do not require immediate support to areas with increased demands. (e.g. skeletal muscles, heart).
  • Venoconstriction with decreased blood flow is the mechanism for a decrease in splanchnic blood flow during exercise
Quiet standing
Cardiac Output 5900 24000
Blood flow to:
Heart 250 1000
Brain 750 750
Active skeletalmuscle 650 20850
Inactive skeletal 'muscle 650 300
Skin 500 500
Kidney, liver, GIT 3100 600
  • The lymphatic system. unlike the circulatory system, has no pump to move lymph fluid. Any form of exercise that incorporates major muscle groups and deep breathing will encourage lymph flow. Muscle movement squeezes lymph vessels.
CHANGES IN MUSCLE BLOOD FLOW DURING EXERCISE
  • The blood flow of resting skeletal muscle is low (2-4 ml./100 g/inin). The muscle blood flow can increase a maximum of about 25 fold during the most strenuous exercise.Amount of blood flow to skeletal muscles during exercise : 50 to 75 mL/min of blood per 100 g of muscle.
  • Almost one half of this increase in flow is due to intramuscular vasodilatation caused by the direct effects of increased muscle metabolism.
  • The remaining increase results from multiple factors, the most important of which is probably the moderate increase in arterial blood pressure.
  • The local mechanisms maintaining a high blood flow in exercising muscle include a fall in tissue P02, a rise in tissue PCO2, and accumulation of K+, and other vasodilator metabolites. The rise in temperature further dilates the vessels.
  • The increase in blood flow is instantaneous.
ISOMETRIC AND ISOTONIC EXERCISES
  • CVS changes in Isometric exercise :
  • Heart rate rises
  • Systolic and diastolic blood pressure rises sharply
  • Stroke volume changes relatively little.
  • Cardiac output increases.
  • The relative increases in cardiac output and mean blood pressure are such that calculated systemic vascular resistance is unchanged.
  • Patients wit ventricular arrhythmia or myocardial infarction should avoid this as tey can increase their intensity.
  • S3,S4 is accentuated
  • Diastolic murmur of Mitral stenosis becomes louder
  • Diastolic murmur of aortic regurgitation,systolic murmur of mitral regurgitation and ventricular septal defect increases.
  • Systolic murmur of aortic stenosis and systolic murmur of hypertrophic obstructive cardiomyopathy diminishes.
CVS changes in Isotonic exercise(Type of exercise done to increase the muscle strength)
  • Heart rate rises
  • Stroke volume increases markedly
  • Peripheral resistance decreases d/t vasodilation in exercising muscle
  • Systolic b.p. rises only moderately, whereas diastolic pressure usually remains unchanged or falls.
  • Cardiac output increases
SUMMARY OF RESPONSES TO EXERCISE
Heart rate ↑↑

Stroke volume
Pulse pressure ↑ (increased stroke volume)
Cardiac output,Venous return ↑↑

↑ (slight)
Mean arterial pressure
Total peripheral resistance (TPR) ↓↓ (vasodilation in skeletal muscle)
Arteriovenous O2 difference ↑↑ (increased O2 consumption by tissues)
O2 consumption
CO2 production
Ventilation rate
Pulmonary venous resistance Decreases
Arterial Po2 and Pco2 No change
Arterial pH No change during moderate exercise; ↓ During strenuous exercise
Venous Pco2
Pulmonary blood flow & cardiac output
V/Q ratio More evenly distributed throughout the lung
Physiologic dead space
O2-hemoglobin dissociation curve Shifts to the right; ↑ P50; decreased affinity
  • During heavy exercise cardiac output increases 4-5 fold, but there is only a small rise in pulmonary arterial pressure, due to the increase in cross sectional area of pulmonary vasculature as a result of opening up of the capillaries.
  • Body temperature increases with exercise.
  • Hyperventilation in the beginning and Hyperkalemia are seen during severe exercise.
  • Isocapnic exercise is Breathing of increased volume of ventilation for long period.
Exam Question
  •  Body temperature increases during exercise.
  • In isometric exercise following parameters are increased :Heart rate , Cardiac output ,Mean arterial pressure.
  • Patients with Ventricular Arrhythmia or Myocardial infarction should avoid Isometric exercises.
  • S3,S4 is accentuated due to isometric exercise.
  • Effects on murmur due to Isometric exercise:
  • Diastolic murmur of Mitral stenosis becomes louder
  • Diastolic murmur of aortic regurgitation,systolic murmur of mitral regurgitation and ventricular septal defect increases.
  • Systolic murmur of aortic stenosis and systolic murmur of hypertrophic obstructive cardiomyopathy diminishes.
  • Cerebral blood flow does not change due to the effect of moderate exercise.
  • During heavy exercise the cardiac output (CO) increases upto five fold while pulmonary arterial pressure rises very little. This physiological ability of the pulmonary circulation is best explained by increase in the number of open capillaries.
  • Venoconstriction with decreased blood flow is responsible for a decrease in splanchnic blood flow during exercise.
  • Amount of blood flow to skeletal muscles during exercise : 50 to 75 mL/min of blood per 100 g of muscle.
  • During exercise increase in 02 delivery to muscles is because of Increased stroke volume , Increased extraction of oxygen from the blood , Increased blood flow to muscles. Blood supply during exercise is increased in coronary circulation.
  • A right shift of Hb - 02 dissociation curve is seen in excercising muscle. Increase blood supply to muscle , Increase stroke volume , Increase O2 extraction are seen due to exercise.
  • Hyperventilation in the beginning and Hyperkalemia are seen during severe exercise.
  • Type of exercise done to increase the muscle strength is Isotonic.
  • Isocapnic exercise is Breathing of increased volume of ventilation for long period.
  • Factors responsible for blood supply increase in muscle during exercise : Local metabolite ,Sympathetic stimulation, Cholinergic stimulation
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