EFFECTS OF EXERCISE ON RESPIRATION

Muscular exercise brings about a lot of changes on various systems of the body. Degree of changes depends upon the severity of exercise.

EFFECTS OF EXERCISE ON RESPIRATION

EFFECT ON PULMONARY VENTILATION

Pulmonary ventilation is the amount of air that enters and leaves the lungs in 1 minute. It is the product of tidal volume and respiratory rate. It is about 6 liter/minute, with a normal tidal volume of 500 mL and respiratory rate of 12/minute. During exercise, hyperventilation, which includes increase in rate and force of respiration occurs. In moderate exercise, respiratory rate increases to about 30/minute and tidal volume increases to about 2,000 mL. Thus, the pulmonary ventilation increases to about 60 L/ minute during moderate exercise. In severe muscular exercise, it rises still further up to 100 L/minute.

Factors increasing pulmonary ventilation during exercise

1. Higher centers

2. Chemoreceptors

3. Proprioceptors

4. Body temperature

5. Acidosis.

1. Higher Centers

Rate and depth of respiration increase during the onset of exercise. Sometimes, before starting the exercise, thought or anticipation of exercise itself increases the rate and force of respiration. It is a psychic phenomenon due to the activation of higher centers like Sylvian cortex and motor cortex of brain. Higher centers, in turn accelerate the respiratory processes by stimulating respiratory centers.

2. Chemoreceptors

Chemoreceptors which are stimulated by exerciseinduced hypoxia and hypercapnea, send impulses to

the respiratory centers. Respiratory centers, in turn increase the rate and force of respiration.

3. Proprioceptors

Proprioceptors, which are activated during exercise, send impulses to cerebral cortex through the somatic afferent nerves. Cerebral cortex, in turn causes hyperventilation by sending impulses to the medullary respiratory centers

4. Body Temperature

Body temperature which increases by muscular activity, increases the ventilation by stimulating the respiratory centers.

5. Acidosis

Acidosis developed during exercise also stimulates the respiratory centers, resulting in hyperventilation.

EFFECT ON DIFFUSING CAPACITY FOR OXYGEN

Diffusing capacity for oxygen is about 21 mL/minute at resting condition. It rises to 45 to 50 mL/minute during moderate exercise because of increased blood flow through pulmonary capillaries.

EFFECT ON CONSUMPTION OF OXYGEN

Oxygen consumed by the tissues, particularly the skeletal muscles is greatly enhanced during exercise.

Because of vasodilatation in muscles during exercise, more amount of blood flows through the muscles and more amount of oxygen diffuses into the muscles from blood. The amount of oxygen utilized by the muscles is directly proportional to the amount of oxygen available.

EFFECT ON OXYGEN DEBT

Oxygen debt is the extra amount of oxygen required by the muscles during recovery from severe muscular exercise. After a period of severe muscular exercise, amount of oxygen consumed is greatly increased. Oxygen required is more than the quantity available to the muscle. This much of oxygen is required not only for the activity of the muscle but also for reversal of some metabolic processes such as:

1. Reformation of glucose from lactic acid, accumulated during exercise

2. Resynthesis of ATP and creatine phosphate

3. Restoration of amount of oxygen dissociated from hemoglobin and myoglobin.

Thus, for the above reversal phenomena, an extra amount of oxygen must be made available in the body

after severe muscular exercise. Oxygen debt is about six times more than the amount of oxygen consumed under resting conditions.

EFFECT ON VO2 MAX

VO2 max is the amount of oxygen consumed under maximal aerobic metabolism. It is the product of

maximal cardiac output and maximal amount of oxygen consumed by the muscle.

In a normal active and healthy male, the VO2 max is 35 to 40 mL/kg body weight/minute. In females, it is 30 to 35 mL/kg body weight/minute. During exercise, VO2 max increases by 50%.

EFFECT ON RESPIRATORY QUOTIENT

Respiratory quotient is the molar ratio of carbon dioxide production to oxygen consumption. Respiratory quotient in resting condition is 1.0 and during exercise it increases to 1.5 to 2. However, at the

end of exercise, the respiratory quotient reduces to 0.5.

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