WHO grading of exercise (1978)
- Heart rate
- Stroke volume
- Cardiac output
- Blood pressure
- Blood flow
- Blood volume
1) Heart Rate
There is a linear increase in heart rate during exercise
Maximum heart rate achievable is 220 – Age
Reduction in heart rate during exercise in seen in
- Advanced age which leads to decrease in biological functions
- Physical training
Physical Training
Physical training decreases the resting heart rate due to
- Increase in Parasympathetic tone
- Decreased psychic stimuli leading to decreased sensitivity to sympathetic receptors
Heart rate increases during exercise due to
- Neurogenic cause
- Circulating hormones
- Increase in body temperature
- Chemical changes
Neurogenic cause
Central reflexes
- Psychic stimuli: Activity of limbic system & motor cortex directly stimulate medulla
- Decrease in Vagal tone
Peripheral reflexes
- Muscle spindle
- Muscle tendon receptors
- Organ of corti
Circulating hormones
- Catecholamines from adrenal medulla
- Thyroxine from thyroid gland
Increase in body temperature
- Increases stimulation of SA node
- Increases metabolic activities
Chemical changes
- Decrease in arterial pO2
- Increase in arterial pCO2
- Decrease in pH
2) Stroke Volume
Normal stroke volume is 80-90 ml
It increases by two times during exercise due to
- Increase in venous return
- Increase in myocardial contractility
Increase in venous return us due to:
- Muscle pump
- Negative intra-thoracic pressure
- Modification of tone in the capacitance vessels
 |
| Increase in Venous return |
Increase in Myocardial contractility is due to:
- Release of Ephidrine and Norephidrine from the sympathetic system and adrenal medulla
- HR>120/min, but there is no increase in stroke volume
 |
Increase in Myocardial contractility |
3) Cardiac Output
Normal Cardiac Output is 5-6 liters
During maximum exercise, the Cardiac Output increases upto 5 to 6 times due to:
- Increase in Heart rate
- Increase in Stroke volume
Higher values of maximum cardiac output is achieved by young adults is
due to higher maximum attainable heart rate
4) Blood Pressure
Blood Pressure in Systemic Circulation
Systolic Blood Pressure
Increases linear with severity of exercise (up to 200mmHg) which is due to:
- Increase in Cardiac output
- Vasoconstriction in non-working muscles
There is no change in Diastolic Blool Pressure in mild and moderate exercise because of drastic vasodilation in working muscles
There is slight in Distolic Blood Pressure during severe exercise because of vasoconstriction in nonworking muscles and skin
Mean Blood Pressure (MBP)
Increases from 90 mmHg to 140 mmHg
Blood Pressure in Pulmonary Circulation
SBP: 15-20 mmHg, DBP: 5-8 mmHg, MBP: 8-12 mmHg
Mild and moderate exercise
- Mild increase in mean blood pressure
Heavy exercise
- Marked increase in mean blood pressure
5) Blood flow
Muscle blood flow
Resting: 3-4 mL/100gm/min.
Heavy exercise: increases 25-30 times (100 mL/100gm/min.), due to
- Increase in capillary density (opening of more capillaries)
Increase in muscle blood flow starts before the exercise and reaches a plateau in 2 minutes
When a contracting muscle develop more than 70% of its
maximal tension, blood flow is completely stopped as a result of compression of
its blood vessels
Coronary Blood Flow
During rest: 250 Ml/min
During maximum exercise: increases 5 times due to:
- Increased coronary blood flow
- Coronary vasodilation done by Catecholamines, hypoxia, fall in blood pH, ATP and ADP
Pulmonary Blood Flow
Rest: 350-800 mL/min.
Heavy exercise: Increases linearly with increase in cardiac output
Skin Blood Flow
Resting: 500 mL/min.
Slight decreases in beginning of the exercise due to reflex vasoconstriction
Later increases 7 times due to stimulation of hypothalamus secondary to increase in body temperature leading to vasodilatation and helps heat loss and transport of metabolites
Server exercise: decreases due to vasoconstriction of skin blood
vessels
Adipose Tissue Blood Flow
Increases 4 times during exercise
Advantage
- Helps to deliver fatty acids mobilized from triglyceride stores to the working muscles
Brain Blood Flow
During rest: 750 mL/min.
During exercise: No change during any grade of exercise
Visceral Blood Flow
6) Blood Volume
15% decrease in blood volume causing haemoconcentration due to
- Increase in Hydrostatic pressure in capillaries causing loss of plasma water
- Accumulation of osmotically active metabolites in tissue spaces (potassium, phosphate, lactic acid) causing drainage of plasma water from capillaries
Advantages:
- O2 carrying capacity of blood increases because of increase in concentration of RBCs
- Increased acid buffering capacity due to increase in plasma proteins
Disadvantages:
- Increase in viscosity of blood → Reduction in blood flow
- WBC count increases, due to washing out of WBCs from storage places and bone marrow
Summary
