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 |
CHANGES IN BLOOD & LYMPHATIC FLOW DURING EXERCISE:
BLOOD FLOW:
- Blood is shunted to regions requiring immediate support to meet increasing demands.
– E.g. Skeletal muscles, heart.
- Decreased splanchnic blood flow.
– Due to venoconstriction.
- Cerebral blood flow remains constant.
- Despite small rise in systemic blood pressure.
- Pulmonary hyperventilation causes hypocapnia.
- Ultimately causes local cerebral vasoconstriction.
- Lymphatic system has no pump to move lymph fluid.
- Increased lymphatic flow seen,
– In major muscle groups with all types of exercise severity.
– Also with deep breathing.
- Muscle movement squeezes lymph vessels.
|
Event |
Quiet standing |
|
|
Cardiac Output |
5900 |
24000 |
|
Blood flow to: |
|
|
|
Heart |
250 |
1000 |
|
Brain |
750 |
750 |
|
Active skeletal muscle |
650 |
20850 |
|
Inactive skeletal ‘muscle |
650 |
300 |
|
Skin |
500 |
500 |
|
Kidney, liver, GIT |
3100 |
600 |
In resting skeletal muscle:
- Blood flow is low
- 2-4 ml./100 g/min.
During exercise:
- Skeletal muscle blood flow –
- 50 to 75 mL/min of blood per 100 g of muscle
During strenuous exercise:
- Blood flow increases 25-fold.
Causes of increased blood flow:
- Intramuscular vasodilatation.
– Directly due to increased muscle metabolism.
- Moderate increase in arterial blood pressure.
- Fall in tissue P02.
- Rise in tissue PCO2.
- Hyperkalemia.
- Vasodilator metabolites.
- Increased temperature.
– Further dilating vessels.
CHANGES DURING ISOMETRIC & ISOTONIC EXERCISES
CVS changes in Isometric exercise:
In healthy individual:
- Heart rate rises.
- Sharp rise in systolic & diastolic blood pressure.
- Cardiac output increases.
– Relative increase in cardiac output & mean blood pressure maintains calculated systemic vascular resistance.
- S3, S4 is accentuated
- Stroke volume changes relatively little.
- Louder murmur especially,
– Diastolic murmur of mitral stenosis & aortic regurgitation.
– Systolic murmur of mitral regurgitation.
- Increases ventricular septal defect.
- Diminishing murmur especially,
– Systolic murmur of aortic stenosis & hypertrophic obstructive cardiomyopathy.
- Avoid isometric exercise in patients with,
– Ventricular arrhythmia.
– Myocardial infarction.
– Due to risk of increasing intensity.
CVS changes in Isotonic exercise:
- Isotonic exercise: Done to increase muscle strength
- Heart rate rises.
- Stroke volume increases markedly
- Peripheral resistance decreases,
– Due to vasodilation.
- Systolic pressure rises only moderately.
- Diastolic pressure remains unchanged/falls.
- Cardiac output increases
SUMMARY OF RESPONSES TO EXERCISE
| Heart rate |
↑↑
↑ |
| Stroke volume | |
| Pulse pressure | ↑ (increased stroke volume) |
| Cardiac output Venous return |
↑↑
In Heavy exercise, cardiac output increases 4-5 fold ↑ ↑ (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 |
↑
↑ More evenly distributed throughout the lung |
| Pulmonary blood flow & cardiac output | |
| V/Q ratio | |
| Physiologic dead space | ↓ |
| O2-hemoglobin dissociation curve | Shifts to the right; ↑ P50; decreased affinity |
- Body temperature increases with exercise.
- Hyperventilation in beginning.
- Hyperkalemia seen during severe exercise.
- Isocapnic exercise is breathing increased volume of ventilation for long period.
- Cerebral blood flow remains constant.
Exam Important
- 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.
- Accentuated S3, S4 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 & of hypertrophic obstructive cardiomyopathy diminishes.
- Cerebral blood flow does not change due to the effect of moderate exercise.
During heavy exercise
- Cardiac output (CO) increases up to fivefold.
- Pulmonary arterial pressure rises very little.
- This physiological ability of the pulmonary circulation is best explained by the 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 O2 delivery to muscles due to,
– Increased stroke volume.
– Increased extraction of oxygen from blood.
– Increased blood flow to muscles
- During exercise, there is increased coronary circulation.
- A right shift of Hb – O2 dissociation curve is seen in exercising muscle.
- Increase blood supply to muscle, increase stroke volume & increased O2 extraction is seen due to exercise.
- Hyperventilation in beginning & Hyperkalemia in later stages is 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
Click Here to Start Quiz
