Why is Cardio Important? – Effects on the Body

Have you ever sat down and thought why is cardio important? Why am I doing this? Then you’re not alone! There are countless reasons why cardio is important, both short and long-term. In this article, we will discuss the different ways that your body changes when you begin to exercise.

We will also look at how these changes can impact your overall health and well-being. So, whether you’re just starting out or have been working out for years, read on to learn more about the amazing effects that cardio has on your body!

Short Term Effects of Exercise On The Body

As you exercise, oxygen demand from your muscles drastically increases. Therefore, there is a need for more blood flow to the particular muscles being used when exercising. But how much of an increase is there?

Well, if we were to look at a muscle at rest, and look at the average blood flow, we would see that it is about 3-4 milliliters per minute per 100g of muscle tissue. When we exercise, this can increase up to 200 milliliters per minute per 100g of muscle tissue. There have even been measurements in the quadriceps of elite marathon runners of changes of up to 400 milliliters per minute per 100g of muscle tissue – providing why cardio is important and has long-lasting effects on the body. So in extreme cases, that’s a 100x increase in blood flow to a muscle!

There are 3 big ways the body achieves this increase in blood flow called circulatory adjustments. Those are:

1. An increase in cardiac output
2. Vasoconstriction of peripheral arterioles
3. Forceful contraction of the muscular walls of the veins

You may not understand what each of those terms means, so let’s go through them one by one:

Why is Cardio Important for the Heart? How Cardiac Output Changes During Exercise

Cardiac output refers to the amount of blood pumped out of the heart in one minute. There are 2 main factors that influence this:

1. Heart rate or BPM (heartbeats per minute)
2. Stroke volume (volume of blood pumped with each beat)

Both of the above, heart rate and stroke volume, increase when we do exercise. We are all familiar with the idea that when we are running around and exercising, our heart rate will go up. During intense cardio activity, we can see heart rates reach highs of 200 beats per minute (BPM).

You may have heard of the general rule for calculating a person’s maximum heart rate which is 220 minus a person’s age. For example, if someone is 25 years old, the rough expected maximum heart rate for that individual would be 195 BPM.

The stroke volume of your heart refers to the volume of blood that is pumped out of your heart with each beat. The force of your heart’s left ventricle (the main chamber of the heart in which blood is pumped out from) is roughly doubled during exercise. Therefore, the volume of blood that is pumped out of your heart with each beat will increase.

The average adult male has a cardiac output of 5.6 liters per minute when at rest. Females of the same age will have about 4.9 liters per minute when at rest.

As an example, let’s say we took someone who isn’t exercising consistently, their heart’s cardiac output can go up to around 13-15 liters per minute during exercise. So roughly a 3x increase.

However, people who are consistently exercising and who are extreme athletes can see their cardiac output increase to somewhere in the 30-40 liter range per minute.

These are amazing adjustments the heart can make when meeting the demands put on the body when consistently exercising over a longer period of time, and why cardio is important, but we’ll get onto the longer-term adaptions the body makes when undergoing consistent cardio training later.

How the Body Prioritizes Blood Supply during exercise

Another change your body undergoes when performing physical training is your body reduces the blood supply to areas of your body where it is not as needed as the muscles which are currently working.

The smaller arteries called arterioles constrict and narrow, reducing blood supply to non-muscular tissue such as the intestines or the skin. The body does this to temporarily lend more blood to the muscle tissue that is exercising at the given moment.

For example, if you were performing squats, your body is going to prioritize getting blood to your legs rather than your intestines because digesting food isn’t a priority at that time.

There are two exceptions regarding this vasoconstriction during exercise:

1. The brain. It doesn’t make sense for your body to restrict blood flow to the brain because the brain is needed to coordinate skeletal muscle activities.
2. The heart. The coronary arteries are something your body definitely doesn’t want to restrict as these blood vessels go to the heart itself to stay open so cardiac operation can remain at current levels.

Why Your Veins Constrict During Exercise

When it comes to our blood vessels, there is a key difference between arteries and veins. Arteries and arterioles take blood away from the heart whereas venules and veins take the blood back to the heart.

During cardiovascular exercise, the walls of the veins contract forcefully to increase the blood flow going back to the heart. This increases the volume of blood being returned to the heart which means more blood being pumped out of the heart in order to carry more oxygen to your muscles.

Long Term Body Adaptations Due to Cardio

So how can an elite-level athlete push 400 milliliters per minute per 100g of muscle into their muscles and have a cardiac output of 30-40 liters per minute? And why is cardio important?

A big part of that answer lies within the myocardium of the heart. The myocardium is essentially the heart muscle tissue that does all the pumping. In elite athletes, we have seen myocardium mass increases of 50-75%. This means an athlete’s heart will be thicker and stronger than an average person’s.

Myocardium muscle tissue is made up of multiple cardiac muscle cells. Generally, when muscle tissue gets bigger, it can be due to two different factors: the muscle cells we already have can get bigger or there can be an increase in the number of muscle cells.

The muscle cells which make up the myocardium cannot divide or undergo mitosis. As a side note, this is why heart attacks are so dangerous because any muscle cells which are killed in the heart attack cannot be replaced and typically get replaced by scar tissue instead.

This means the heart can only increase the size of the muscle cells it has, by undergoing a process called hypertrophy. A larger cell is a stronger cell, so overall the heart muscle gets stronger and therefore can contract more forcefully and increase the cardiac output.

A real-world example: let’s say you are training for a marathon and in the initial stages of training you get to a steady pace and your heart is pumping at 160 beats per minute. Over time, as your heart muscle (myocardium) gets stronger, you will be able to keep that same pace at a lower heart rate.

This is because as the heart gets bigger and stronger, the stroke volume increases, which means each individual heartbeat is able to pump blood. This is also why people who begin to become physically active will start to see a decrease in their resting heart rate.

The other long-term adaptation we might see is microvascularization. In other words, the blood flow to the muscle tissue. Muscles receive oxygen from the blood through blood vessels called capillaries. As someone exercises, the number of capillaries increases. Therefore, you have more blood being able to penetrate the muscle tissue.

Why is Cardio Important for Weight Loss?

Cardio is important for weight loss because it helps to increase the number of calories you burn. The more calories you burn, the more weight you will lose. Cardio also helps to improve your metabolism, which means you will burn more calories even when you are not exercising.

Cardio is also important for weight loss because it helps to reduce the amount of fat in your body. Fat is stored in the body in adipose tissue. Adipose tissue is made up of cells called adipocytes. These cells store fat in the form of triglycerides. When your body needs to use the energy it is storing as fat, it breaks down the triglycerides in the adipocytes. Which results in a reduction of fat mass.

Another reason cardio is also important for weight loss is that it can help to reduce your appetite. When you exercise, your body releases hormones that can help to suppress the appetite. This means you will be less likely to overeat that day and gain weight.

Summary

Cardio is an important part of a healthy lifestyle. It has many benefits for the body, both in the short term and the long term. Cardio can help to increase the number of calories you burn, improve your metabolism, strengthen your heart (which has many health benefits), and reduce the amount of fat in your body.

Sources

• Increased myocardial mass and attenuation of myocardial strain in professional male soccer players and competitive male triathletes – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7568698/
• Influence of increased left ventricular myocardial mass on early and late mortality after cardiac surgery – https://academic.oup.com/bja/article/110/1/41/274195
• Magnetic resonance imaging of athlete’s heart: myocardial mass, left ventricular function, and cross-sectional area of the coronary arteries – https://pubmed.ncbi.nlm.nih.gov/10663764/
• The Role of Exercise and Physical Activity in Weight Loss and Maintenance – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3925973/