Understanding VO2max and Aerobic Fitness

VO2max is the maximal amount of oxygen consumed in one minute and is the measure of aerobic fitness. So, how does exercise training increase VO2max or aerobic fitness? The Fick equation describes the factors affecting VO2max as follows. VO2max equals heart rate max times stroke volume max times delta arteriovenous oxygen content. Thus, VO2 max can be increased by increasing one of these three variables. However, exercise training does not increase or affect maximal heart rate. Thus, exercise training is able to increase VO2 max two ways. The first is by increasing stroke volume. This increases the amount of blood circulated per minute. The second way is by increasing the arteriovenous oxygen difference. The way this difference is increased is by increasing the amount of blood circulated per minute. increasing the amount of oxygen taken out of the blood and taken up by the tissues. Thus, exercise training both increases the amount of oxygen available to the cells and exercise training increases the uptake of oxygen by the cells. How would exercise training cause these changes to occur? First, the increase in stroke volume will be examined. Stroke volume is the amount of blood that leaves the heart in one beat. Stroke volume increases from aerobic exercise training due to the heart growing larger. The question may arise at this point, isn't growing a larger heart a dangerous condition and can lead to deadly conditions such as heart failure? The answer lies in the fact that there is more than one way for the heart to grow. The heart can grow from pathological hypertrophy or physiologic hypertrophy. Pathological hypertrophy can be the result of a thickening of the wall of the heart. This thickening can be so great that it is difficult for the heart to contract or for the heart cells to receive adequate oxygen. leading to poor circulation and the death of heart cells. This is why the growth is termed pathologic as it can cause a diseased heart. Physiologic hypertrophy is the beneficial growth from the heart that can occur from exercise training. In physiologic hypertrophy, the myocardium, which is the muscle layer of the heart, grows in series. This means new contractile units are added to the end of cardiac myocytes, which are the cells of the myocardium, like adding links to a chain to make the chain longer. By increasing the length of the myocyte, the chamber of the ventricle grows larger. The now larger ventricle is able to take in more blood than it could previously. There are also some contractile units grown in parallel, meaning the myocardium or wall of the heart becomes thicker. So how is it that the wall becomes thicker just as in pathologic hypertrophy but in physiologic hypertrophy, the wall thickening does not cause disease? The answer lies in the ventricular chamber radius to wall thickness ratio. For example, if the radius of the chamber of the left ventricle is 2 cm and the wall thickness is 1 cm, the ratio of chamber radius to wall thickness is 2. In pathologic hypertrophy, the chamber may not grow at all, but the wall will get thicker. Thus, the chamber radius may remain 2 cm while the wall may thicken to 1.75 cm. The chamber radius to wall thickness ratio is now 1.14, far less than 2. In the case of physiologic hypertrophy, the chamber radius and wall thickness increase together. Since the growth is both in series and in parallel in physiologic hypertrophy of the myocardium, it means both the chamber is growing larger and the wall is getting thicker. But the growth of both remains proportionate. For example, the chamber radius may increase from 2 cm to 3 cm, and the wall thickness may increase from 1 cm to 1.5 cm. Dividing 2 cm by 1 cm and 3 cm by 1.5 cm, both results in a chamber radius to wall thickness ratio of 2. Thus, one crucial way physiologic hypertrophy differs from pathologic hypertrophy is that physiological hypertrophy is growth of the myocardium and the adenomyosis. that maintains the chamber radius to wall thickness ratio. But how does this increase VO2 max? As the chamber that holds the blood grows larger, the heart is able to take in more blood than it could before. However, increasing the volume of blood the heart must push out would not be beneficial without increasing the strength of the heart to push out the blood. Since physiologic hypertrophy grows the heart both in series and in parallel, it means the heart grows larger to accommodate more blood. while proportionately growing stronger to push out the blood. By maintaining the chamber radius to wall thickness ratio, it means that the heart grows proportionately in size as it does in strength. This allows for a match between the amount of blood the heart can hold and the amount of strength the heart has to eject blood. Another distinction between pathologic and physiologic hypertrophy is the increase in oxygen availability to the myocardium. In response to aerobic exercise training, as the myocardium grows larger, new capillaries grow as well to the point that there is an increase in the number of capillaries around the myocardium. Similar to the concept of proportionality just explained, the benefit of the increased number of capillaries to the myocardium is to ensure as the myocardium grows larger, there is a proportionate increase in oxygen supply to the myocardium. So, how does exercise training increase the arteriovenous oxygen difference? In a similar manner as just described in the myocardium, except for skeletal muscle instead. The increase in difference in arterial versus venous oxygen content largely is the result of angiogenesis. Angiogenesis is the growth of new blood vessels. In some instances, there can be as much as a 60% increase in the number of capillaries surrounding a skeletal muscle cell as compared to before exercise training. How does this increase VO2max? One adaptation from aerobic exercise training is that the blood can carry more oxygen than the blood of a human. than it could before training. Erythropoietin, or EPO, which is often secreted as a result of aerobic exercise stimulates the bone marrow to increase the production of red blood cells. Increasing the number of red blood cells increases the amount of oxygen the blood can carry. By increasing the number of blood vessels surrounding the muscle cells, along with increasing the number of red blood cells, there is an increase in the exposure of the muscle cell to oxygen. The increase in blood vessels surrounding the muscle cell also allows blood to move more slowly, increasing the amount of time for oxygen to diffuse out of the blood and into the cells. Additionally, the increased number of capillaries decreases the diffusion distance the oxygen must travel to reach the cells. Lastly, there is an increase in mitochondria in the muscle cells after exercise training which leads to a decrease in oxygen content in the cell. This increases the concentration gradient between the amount of oxygen in the blood and the amount of oxygen in the cell which allows the oxygen to be distributed more efficiently. to move more quickly out of the blood and into the cells. Therefore, exercise training increases the amount of oxygen in the blood, increases the exposure time of the oxygen to the cells, decreases the distance the oxygen must travel to reach the cells, and increases the rate at which oxygen can enter the cells. Coupling the increased difference in arteriovenous oxygen content with the increase in stroke volume leads to an increase in oxygen consumption per minute, which increases VO2 max. Thanks for watching and remember to subscribe to our channel for the latest video.

VO2max equals heart rate max times stroke volume max times delta arteriovenous oxygen content. Thus, VO2 max can be increased by increasing one of these three variables. However, exercise training does not increase or affect maximal heart rate. Thus, exercise training is able to increase VO2 max two ways. The first is by increasing stroke volume.

This increases the amount of blood circulated per minute. The second way is by increasing the arteriovenous oxygen difference. The way this difference is increased is by increasing the amount of blood circulated per minute.

increasing the amount of oxygen taken out of the blood and taken up by the tissues. Thus, exercise training both increases the amount of oxygen available to the cells and exercise training increases the uptake of oxygen by the cells. How would exercise training cause these changes to occur?

First, the increase in stroke volume will be examined. Stroke volume is the amount of blood that leaves the heart in one beat. Stroke volume increases from aerobic exercise training due to the heart growing larger. The question may arise at this point, isn't growing a larger heart a dangerous condition and can lead to deadly conditions such as heart failure?

The answer lies in the fact that there is more than one way for the heart to grow. The heart can grow from pathological hypertrophy or physiologic hypertrophy. Pathological hypertrophy can be the result of a thickening of the wall of the heart.

This thickening can be so great that it is difficult for the heart to contract or for the heart cells to receive adequate oxygen. leading to poor circulation and the death of heart cells. This is why the growth is termed pathologic as it can cause a diseased heart.

Physiologic hypertrophy is the beneficial growth from the heart that can occur from exercise training. In physiologic hypertrophy, the myocardium, which is the muscle layer of the heart, grows in series. This means new contractile units are added to the end of cardiac myocytes, which are the cells of the myocardium, like adding links to a chain to make the chain longer. By increasing the length of the myocyte, the chamber of the ventricle grows larger.

The now larger ventricle is able to take in more blood than it could previously. There are also some contractile units grown in parallel, meaning the myocardium or wall of the heart becomes thicker. So how is it that the wall becomes thicker just as in pathologic hypertrophy but in physiologic hypertrophy, the wall thickening does not cause disease? The answer lies in the ventricular chamber radius to wall thickness ratio. For example, if the radius of the chamber of the left ventricle is 2 cm and the wall thickness is 1 cm, the ratio of chamber radius to wall thickness is 2. In pathologic hypertrophy, the chamber may not grow at all, but the wall will get thicker.

Thus, the chamber radius may remain 2 cm while the wall may thicken to 1.75 cm. The chamber radius to wall thickness ratio is now 1.14, far less than 2. In the case of physiologic hypertrophy, the chamber radius and wall thickness increase together. Since the growth is both in series and in parallel in physiologic hypertrophy of the myocardium, it means both the chamber is growing larger and the wall is getting thicker. But the growth of both remains proportionate.

For example, the chamber radius may increase from 2 cm to 3 cm, and the wall thickness may increase from 1 cm to 1.5 cm. Dividing 2 cm by 1 cm and 3 cm by 1.5 cm, both results in a chamber radius to wall thickness ratio of 2. Thus, one crucial way physiologic hypertrophy differs from pathologic hypertrophy is that physiological hypertrophy is growth of the myocardium and the adenomyosis. that maintains the chamber radius to wall thickness ratio. But how does this increase VO2 max?

As the chamber that holds the blood grows larger, the heart is able to take in more blood than it could before. However, increasing the volume of blood the heart must push out would not be beneficial without increasing the strength of the heart to push out the blood. Since physiologic hypertrophy grows the heart both in series and in parallel, it means the heart grows larger to accommodate more blood.

while proportionately growing stronger to push out the blood. By maintaining the chamber radius to wall thickness ratio, it means that the heart grows proportionately in size as it does in strength. This allows for a match between the amount of blood the heart can hold and the amount of strength the heart has to eject blood. Another distinction between pathologic and physiologic hypertrophy is the increase in oxygen availability to the myocardium.

In response to aerobic exercise training, as the myocardium grows larger, new capillaries grow as well to the point that there is an increase in the number of capillaries around the myocardium. Similar to the concept of proportionality just explained, the benefit of the increased number of capillaries to the myocardium is to ensure as the myocardium grows larger, there is a proportionate increase in oxygen supply to the myocardium. So, how does exercise training increase the arteriovenous oxygen difference?

In a similar manner as just described in the myocardium, except for skeletal muscle instead. The increase in difference in arterial versus venous oxygen content largely is the result of angiogenesis. Angiogenesis is the growth of new blood vessels. In some instances, there can be as much as a 60% increase in the number of capillaries surrounding a skeletal muscle cell as compared to before exercise training.

How does this increase VO2max? One adaptation from aerobic exercise training is that the blood can carry more oxygen than the blood of a human. than it could before training.

Erythropoietin, or EPO, which is often secreted as a result of aerobic exercise stimulates the bone marrow to increase the production of red blood cells. Increasing the number of red blood cells increases the amount of oxygen the blood can carry. By increasing the number of blood vessels surrounding the muscle cells, along with increasing the number of red blood cells, there is an increase in the exposure of the muscle cell to oxygen.

The increase in blood vessels surrounding the muscle cell also allows blood to move more slowly, increasing the amount of time for oxygen to diffuse out of the blood and into the cells. Additionally, the increased number of capillaries decreases the diffusion distance the oxygen must travel to reach the cells. Lastly, there is an increase in mitochondria in the muscle cells after exercise training which leads to a decrease in oxygen content in the cell. This increases the concentration gradient between the amount of oxygen in the blood and the amount of oxygen in the cell which allows the oxygen to be distributed more efficiently. to move more quickly out of the blood and into the cells.

Therefore, exercise training increases the amount of oxygen in the blood, increases the exposure time of the oxygen to the cells, decreases the distance the oxygen must travel to reach the cells, and increases the rate at which oxygen can enter the cells. Coupling the increased difference in arteriovenous oxygen content with the increase in stroke volume leads to an increase in oxygen consumption per minute, which increases VO2 max. Thanks for watching and remember to subscribe to our channel for the latest video.

Transcript for:Understanding VO2max and Aerobic Fitness

Transcript for:
Understanding VO2max and Aerobic Fitness