Our cardiovascular system is composed of the heart plus blood vessels, but it also includes surrounding mechanisms which control how the system functions as a whole. This system serves to circulate oxygen, nutrients and waste substances to rightful destinations around the human body.
How well our cardio system functions in our bodies affects all aspects of our overall health and performance. Therefore, it is not surprising that scientists have been researching the links between exercise and cardio health – for a long time.
In this post, we discuss the relationship between physical activity and cardio health. Why is it more important to focus on cardio-respiratory fitness, rather than simply tracking your hours of physical activity?
Next, we focus on the scientific evidence supporting the role of physical activity – specifically in improving heart function. How does the heart adapt to long-term exercise? How are such adaptations healthy for people?
Last, we get practical and ask how can you estimate your day-to-day exercise intensity? Are we exercising enough, towards gaining long-term health benefits?
Part 1: Physical Exercise & Cardio System Benefits
There is very convincing evidence that regular physical activity lowers the risk for cardiovascular disease in individuals [R1].
One study predicted that if all physically inactive people in the world started to exercise, then this would increase worldwide life expectancy by 0.68 years [R2]. This is a significant potential longevity improvement, especially if you consider that life expectancy is a complex measure of human life quality that is quite difficult and slow to improve on a global level.
In 1992, the American Heart Association recognized the fact that “being physical inactive” is a major risk factor for the development of health complications [R3]. Eight years later, the same trusted organization added “physical activity” to the list of key factors for preventing health conditions in people [R4].
1.1 Measuring Fitness Level – the VO2max Bio-Marker
How can we better understand – from a scientific point of view – the cardio health issues that depend on physical activity?
Most scientific studies focus on the concept of Cardio-Respiratory Fitness. The definition of Cardio-Respiratory Fitness considers two components, both of which are essential for improving health and performance:
- how well the heart and blood vessels function to carry blood around the body (the cardio aspect)
- how well the body breathing system manages oxygen which is necessary for aerobic metabolism that life depends on (the respiratory aspect)
When measuring cardiorespiratory fitness, most researchers agree on the value of a biomarker named Maximal Oxygen Consumption – VO2max is the common abbreviation. This marker is important because it is a very good indicator of cardiorespiratory fitness in individuals.
VO2max is measured during intense physical exercise. Once a person reaches his/her top-level oxygen consumption, continuing to exercise (or increasing the intensity of the exercise) will not lead to more oxygen being consumed by the body at any given moment [R5].
When using VO2max as a marker to track fitness levels in study participants, researchers have demonstrated that regular medium- to hard-intensity exercise improves the fitness levels in individuals (as measured by changes in VO2max). Other studies have been specifically carried out on healthy adult participants – who do not regularly exercise. Results from such trials have shown that continuous physical activity for 5 months or longer increases VO2max by approximately 15% to 25% in individuals [R6] & [R7].
The key takeaway is that physical activity drives overall improvement in cardiorespiratory fitness in individuals.
1.2 Cardio-Respiratory Fitness and Health Risks
How is cardiorespiratory fitness important for defining our overall health status?
As far back as the 1980s, there has been solid evidence that greater cardiorespiratory fitness is associated with lower risk of developing cardiovascular disease (CVD) [R8].
In the decades since the links between improving fitness and lower risk for developing CVD have been observed in younger and older, women and men, of different ethnicities.
Because CVD is one of the major health burdens in modern-day societies, this means that if you are able to exercise – you should exercise!
By regularly engaging in physical activity, you are practicing a proven tactic for preventing potential cardio health complications [R9].
As we discussed in the previous section, cardiorespiratory fitness is improved through regular exercise. Because of this, cardiorespiratory fitness levels are often considered as just another way to measure physical activity habits in individuals.
However, studies have revealed that physical activity habits are much better represented by tracking cardiorespiratory fitness, as opposed to people self-tracking and self-reporting their personal exercise patterns [R10].
Moreover, researchers are able to use cardiorespiratory fitness as a strong factor for predicting the odds that cardiovascular disease events occur in individuals.
In fact, cardiorespiratory fitness predicts cardiovascular disease events with greater predictive power, compared to the predictive power of only considering individuals’ physical exercise levels [R11].
Last, it is worth examining the links between not being physically active enough and the risk of developing cardio complications. Researchers measure the level of inactivity as hours of sedentary time per day. Sedentary behavior means not being physically active during this time.
Here is an image that clearly demonstrates the link between daily hours of inactivity and the higher risk for coronary heart disease:
Part 2: Heart Benefits of Physical Activity
Physical activity drives a range of positive effects on the functioning of the heart – the central organ in our cardio system.
Next, we focus on the most important heart muscle processes that occur when people exercise long term.
2.1 Renewal & Growth of Heart Muscle Cells
When you exercise, your heart muscle cells must adapt to the increased work-demands they are presented with.
Over time, regular training stimulates the heart to work more intensively and it enlarges heart muscle cells – known as cardiomyocytes [R13]. This leads to an overall growth in the size of heart muscle tissue as a whole. Importantly, this type of growth is very different from the type of growth that is sometimes caused by health conditions which are harmful to heart tissue [R14].
Even during adulthood, cardiomyocytes retain the ability to divide and multiply [R15]. In fact, nearly half of the heart’s muscle cells are replaced during a normal human lifespan [R16]. Even in adults, physical activity has been shown to support the formation of new cardio muscle cells [R17].
Thus it is important to continue to exercise during our adult life too!
2.2 Lower Rates of Programmed Cell Death in Heart Cells
When heart muscle cells are damaged for whatever biological reason, such cells may be programmed to self-destruct for the benefit of the entire heart muscle tissue. This type of programmed cell death is known as apoptosis and it is a process which plays important roles in the development of heart disease [R18].
Researchers have determined that exercise-driven heart muscle growth does not result in increased levels of apoptosis in heart muscle cells [R19]. On the contrary, exercise protects against heart disease partly because of lower levels of apoptosis in heart muscle cells – in people who regularly exercise [R20].
2.3 Turning Cardiac Stem Cells Into Functional ‘Real’ Heart Cells
One study has suggested that physical activity is associated with increased number of cardiac stem cells [R22]. This process is very eye-catching because newly formed heart cells actually arise from cardiac stem cells – that are present in adults [R23].
In fact, it has been demonstrated that cardiac stem cells exist in the adults, long after people outgrow the embryo development phase that is usually associated with stem cells presence and development [R24].
Because physical activity activates cardiac stem cells to give rise to new cardiomyocytes, researchers have suggested that this process also improves heart muscle regeneration and overall cardio system function [R25].
Part 3: Right Amount of Physical Activity
We all differ in our capacity to undertake physical activity challenges. While some of us are able to exercise at very intense levels, others among us might not be able to tolerate such high-performance demands.
What is the best approach to choosing the right exercise intensity?
To achieve optimal cardio system benefits, high-intensity training is usually recommended for people who are able to withstand it.
If you are not able to train at a high-intensity, remember that it is healthy to engage in moderate-level activity too.
Let us keep in mind that for most people low-intensity physical activity is always better than no physical activity.
How do scientists estimate exercise intensity? And is there a common way to estimate your exercise intensity, without using expensive laboratory equipment?
3.1 Exercise Intensity – VO2max (Scientific Way)
In most clinical studies, proper amounts of exercise are defined as engaging in regular physical activity – for several months in a row.
Most of us can achieve adequate amounts of exercise with moderate-intensity training, such as:
- paced walking
- or cycling
at least 3-4 times a week [R26].
Researchers determine exercise intensity as a percent (%) of the cardiorespiratory fitness marker VO2max [R27]. Therefore, Exercise Intensity = % of VO2max.
Based on this concept, the scientific formula for exercise intensity is:
Moderate Intensity Exercise = 40% to 60% of a person’s VO2max
High-Intensity Exercise = more than 60% of a person’s VO2max Resource: [R28]
Nevertheless, measuring VO2max is somewhat difficult and requires training and laboratory-grade equipment to accurately perform. Therefore, this formula is not very helpful for optimizing your exercise intensity – by yourself and in “everyday-life” circumstances.
In the next section, we discuss an easy and inexpensive way to estimate exercise intensity – all backed by science.
3.2 Exercise Intensity – Measure Heart Rate (Easy ‘Everyday’ Way)
The secret is to use our heart rate as the marker for determining our exercise intensity, as opposed to using VO2max for the same purpose.
How can we adjust the formula for exercise intensity to fit “Our Maximum Heart Rate” instead of “VO2max”?
The estimate for a person’s maximum heart rate is based on a person’s age. You can obtain an estimate of your personal maximum heart rate by subtracting your age from 220.
Therefore, the new simplified formula for measuring exercise intensity is:
Moderate Intensity Exercise Heart Rate = (50% to 70%)*(220 – your current age)
High Intensity Exercise Heart Rate = (70% to 85%)*(220 – your current age) Resource: [R29]
To accurately measure your heart rate during exercise, you will need to use a simple wearable heart rate device or a more advanced fitness monitor. Once you obtain your heart rate while you exercise, you can use the formula above to determine whether you are performing your exercises at a moderate or high intensity.
Example 1: A 50 years old person wishes to exercise at moderate intensity
(0.50 to 0.70 PERCENT) x (220-50 AGE HEART RATE CONVERSION)
= 0.50 x 170 to 0.70 x 170
= 85 to 19 Heart Rate measured in beats per minute
Conclusion: For a 50 years old person to exercise at a moderate-intensity level, a maximum heart rate of 85 to 119 beats per minute is optimal during exercise.
Example 2: A 25 years old person wishes to exercise at high intensity
(0.70 to 0.85 PERCENT) x (220-25 AGE HEART RATE CONVERSION)
= 0.70 x 195 to 0.85 x 195
= 136 to 166 Heart Rate measured in beats per minute
Conclusion: For a 25 years old person to exercise at a high-intensity level, a maximum heart rate of 136 to 166 beats per minute is optimal during exercise.
The simplicity of this approach is that you have a single figure (heart rate) as a threshold you do not want to cross. This can be easily achieved by adjusting the pace of your exercise.
Remember that this is an approximate estimate of exercise intensity and that you should always pay attention to the signals your body sends to you.
You should not push your exercise heart rate above 85% of your estimated maximum heart rate – unless, of course, you are really certain that you can handle it and if you are informed about your health status.
Most importantly, you should respect your body’s capacity and be patient as you keep improving your physical and cardio condition.