Cardiovascular Adjustments During Exercise Notes

Cardiovascular Adjustments During Exercise Introduction

During exercise, there is an increase in the metabolic needs of body tissues, particularly the muscles.

Thus, the various adjustments, which take place in the body, are aimed at:

1. Supply of various metabolic requisites like nutrients and oxygen to muscles and other tissues involved in exercise
2. Prevention of increase in body temperature.

Read And Learn More: Medical Physiology Notes

Types Of Exercise

Exercise is generally classified into two types depending on the type of muscular contraction. The two types of exercise are:

1. Dynamic exercise
2. Static exercise.
3. Cardiovascular changes are slightly different in these two types of exercise.

Dynamic Exercise

• The dynamic exercise primarily involves isotonic muscular contraction. It keeps the joints and muscles moving. Examples are swimming, bicycling, walking, etc.
• External work is involved in this type of exercise. The shortening of muscle fibers against load is called external work.
• In this type of exercise, the heart rate, the force of contraction, cardiac output, and systolic blood pressure increase.
• However, the diastolic blood pressure is unaltered or decreased. It is because, during dynamic exercise, the peripheral resistance is unaltered or decreased depending upon the severity of the exercise.

Static Exercise

• Static exercise involves isometric muscular contraction without the movement of joints.
• An example is pushing a heavy object. This is a type of exercise without the performance of external work.
• During this exercise, apart from an increase in heart rate, a force of contraction, cardiac output, and systolic blood pressure, the diastolic blood pressure also increases.
• It is because of an increase in peripheral resistance during static exercise.

Aerobic And Anaerobic Exercises

Based on the type of metabolism involved, the exercise is classified into two types:

1. Aerobic exercise
2. Anaerobic exercise.

• The terms aerobic and anaerobic refer to the energy-producing process during exercise.
• Aerobic means ‘with air’ or ‘with oxygen’. Anaerobic means ‘without air’ or ‘without oxygen’.
• Both aerobic and anaerobic exercises are required to maintain physical fitness.

Aerobic Exercise

• Aerobic exercise involves activities with lower intensity, which is performed for longer periods.
• The energy is obtained by utilizing nutrients in the presence of oxygen and hence it is called aerobic exercise.
• In the beginning, the body obtains energy by burning glycogen stored in the liver.
• After about 20 minutes, when stored glycogen is exhausted the body starts burning fat.
• Body fat is converted into glucose, which is utilized for energy.
• Aerobic exercise requires a large amount of oxygen to obtain the energy needed for prolonged exercise.

Examples of aerobic exercise:

1. Fast walking
2. Jogging
3. Running
4. Bicycling
5. Skiing
6. Skating
7. Hockey
8. Soccer
9. Tennis
10. Badminton
11. Swimming
12. Rowing.

Anaerobic Exercise

• Anaerobic exercise involves exertion for short periods followed by periods of rest.
• It uses the muscles at high intensity and a high rate of work for a short period.
• The body obtains energy by burning glycogen stored in the muscles without oxygen hence it is called anaerobic exercise.
• Burning glycogen without oxygen liberates lactic acid. Accumulation of lactic acid leads to fatigue.
• Therefore, this type of exercise cannot be performed for a longer period. And a recovery period is essential before going for another burst of anaerobic exercise.
• Anaerobic exercise helps to increase muscle strength.

Examples of anaerobic exercise:

1. Pull-ups
2. Push-ups
3. Weightlifting
4. Sprinting
5. Any other rapid burst of strenuous exercise.

Metabolism In Aerobic And Anaerobic Exercises

• When a person starts doing some exercise like jogging, bicycling, or swimming, the muscles start utilizing energy In order to have quick energy during the first minutes, the muscles burn glycogen stored in them.
• men this period, fat is not burnt. Only glycogen is Md it is burnt without using oxygen.
• This is called anaerobic metabolism. Lactic acid is produced during this period.
• The presence of lactic acid causes some sort of burning sensation in the muscles particularly the muscles of arms, legs, and back.
• The muscles burn all the muscle glycogen within three to five minutes. If the person continues the exercise beyond this, glycogen stored in liver is converted into glucose, which is transported to muscles through blood.
• Now the body moves into aerobic metabolism. The glucose obtained from the liver is burnt in the presence of oxygen.
• No more lactic acid is produced. So the burning sensation in the muscles disappears.
• Proper breathing is essential during this period so that adequate oxygen is supplied to the muscles to extract energy from glucose.
• The supply of glucose from the liver in combination with adequate availability of oxygen allows the person to continue the exercise.
• The utilization of all the glycogen stored in the liver is completed by about 20 minutes.
• If the exercise is continued beyond this, the body starts utilizing the fat. The stored fat called body fat is converted into carbohydrate, which is utilized by the muscles.
• This allows the person to do the exercise for a longer period.

Severity Of Exercise

The cardiovascular and other changes in the body depend upon the severity of exercise.

Based on severity, the exercise is classified into three types.

1. Mild exercise
2. Moderate exercise
3. Severe exercise.

1. Mild Exercise

It is a very simple form of exercise like slow walking. Little or no change occurs in the cardiovascular system during mild exercise.

2. Moderate Exercise

• Moderate exercise does not involve strenuous muscular activity. So, this type of exercise can be performed for a longer period.
• Exhaustion does not occur at the end of moderate exercise. Examples of this type of exercise are fast walking and slow running.

3. Severe Exercise

Severe exercise involves strenuous muscular activity. The severity can be maintained only for a short duration.

Fast running for a distance of 100 or 400 meters is the best example of this type of exercise. Complete exhaustion occurs at the end of severe exercise.

Effects Of Exercise On the Cardiovascular System

1. On Blood

The mild hypoxia developed during exercise stimulates the juxtaglomerular apparatus to secrete erythropoietin.

It stimulates the bone marrow and causes the release of red blood cells. The increased carbon dioxide content in the blood decreases the pH of the blood.

2. On Blood Volume

More heat is produced during exercise and the thermoregulatory system is activated.

This, in turn, causes the secretion of large amounts of sweat leading to:

1. Fluid loss
2. Reduced blood volume
3. Hemoconcentration
4. Sometimes, severe exercise leads to dehydration.

3. On Heart Rate

• Heart rate increases during exercise. Even the thought of exercise or preparation for exercise increases the heart rate.
• It is because of impulses from the cerebral cortex to medullary centers, which reduces vagal tone.
• In moderate exercise, the heart rate increases to 180 beats/minute. In severe muscular exercise, it reaches 240-260 beats/minute.
• The increased heart rate during exercise is mainly because of vagal withdrawal. An increase in sympathetic tone also plays a role.

Four factors are responsible for the increase in the heart rate during exercise:

1. Impulses from proprioceptors, which are present in the exercising muscles; these impulses act through higher centers and increase the heart rate.
2. Increased carbon dioxide tension which acts through medullary centers
3. Rise in body temperature, which acts, on cardiac centers via the hypothalamus: Increased temperature stimulates the SA node directly also
4. The circulating catecholamines are secreted in large quantities during exercise.

4. On Cardiac Output

• Cardiac output increases up to 20 liters/minute in moderate exercise and up to 35 liters/minute during severe exercise.
• The increase in cardiac output is directly proportional to the increase in the amount of oxygen consumed during exercise.
• During exercise, the cardiac output increases because of an Increase in heart rate and stroke volume. Heart safety: increases because of vagal withdrawal.
• Stroke vomits; Increases due to increased force of contraction. Because of vagal withdrawal, sympathetic activity increases leading to an increase in the rate and force of contraction.

5. On Venous Return

Venous return increases remarkably during exercise because of the muscle pump, respiratory pump, and splanchnic vasoconstriction.

6. On Blood Flow To Skeletal Muscles

• There is a great increase in the amount of blood flowing to skeletal muscles during exercise.
• In resting condition, the blood supply to the skeletal muscles is 3-4 mL/100 grams of the muscle/minute.
• It increases up to 60-80 mL in moderate exercise and up to 90-120 mL in severe exercise.
• During muscular activity, stoppage of blood flow occurs when the muscles contract.
• It is because of the compression of blood vessels during contraction. In between the contractions, the blood flow increases.
• Sometimes the blood supply to muscles starts increasing even during the preparation for exercise.
• It is due to sympathetic activity. The sympathetic nerves cause vasodilatation in muscles.
• The sympathetic nerve fibers causing vasodilatation in skeletal muscle are called sympathetic cholinergic fibers since these fibers secrete acetylcholine instead of noradrenaline.
• Several other factors also are responsible for the increase in blood flow to muscles during exercise.
• All such factors increase the amount of blood flow, to muscles by means of dilatation of blood vessels of the muscles.

Such factors are:

1. Hypercapnia
2. Hypoxia
3. Potassium ions
4. Metabolites like lactic acid
5. Rise in temperature
6. Adrenaline secreted from the adrenal medulla
7. Increased sympathetic cholinergic activity.

7. On Blood Pressure

• During moderate isotonic exercise, the systolic pressure is increased. It is due to an increase in heart rate and stroke volume.
• Diastolic pressure is not altered because peripheral resistance is not affected during moderate isotonic exercise.
• In severe exercise involving isotonic muscular contraction, the systolic pressure enormously increases but the diastolic pressure decreases. The decrease in diastolic pressure is because of the decrease in peripheral resistance.
• The decrease in peripheral resistance is due to vasodilatation caused by metabolites.
• During exercise involving isometric contraction, the peripheral resistance increases.
• So, the diastolic pressure also increases along with systolic pressure.

Blood Pressure after Exercise

• Large quantities of metabolic end products are produced during exercise. These substances accumulate in the tissues, particularly the skeletal muscle.
• The metabolic end products cause vasodilatation. So, the blood pressure falls slightly below the resting level after the exercise.
• However, the pressure returns to a resting level quickly as soon as the metabolic end products are removed from the muscles.