The Basics of Cardiovascular Endurance

In Chapter 3, we talked about the five components of health-related fitness. In Chapter 5, we will focus specifically on cardiovascular endurance. Cardiovascular endurance is the ability of the body to transport oxygen to working muscles (Kenny et al., 2015). We are going to talk about cardiovascular fitness as it relates to the average person. A high-level endurance athlete would have a superior level of cardiovascular endurance in order to compete at the level they are competing. With that said, it is important to remember that it is important for non-athletes to at least have a threshold level of cardiovascular endurance for health reasons and to have a good quality of life.

Oxygen Transportation

 Oxygen is transported via the blood throughout the body. The majority of this oxygen is transported through the blood bound to hemoglobin (found in red blood cells) (Kenny et al., 2015). We rely on this oxygen in order to yield energy for our body to do the work it needs to do (note: there are non-oxidative energy sources, but these are only helpful during short bursts). For example, we need oxygen for our heart to contract and for the work needed to digest food. When we exercise, we increase our body’s demand for oxygen because we are doing more work than we are doing at rest! When an individual has better cardiovascular fitness, they are better able to provide the working tissues with enough oxygen to complete the exercise task at hand. For example, if you are running, now you need more blood going to your working muscles so that they are receiving more oxygen! Whether or not you are able to maintain the pace at which you are walking, jogging, or running is dependent on whether your heart, lungs, and blood are able to provide enough oxygen. Someone who is more cardiovascularly fit will be better at doing this and thus may be able to maintain a specific running pace much longer than someone with lower cardiovascular endurance.

Heart Rate

Heart rate is the number of times your heart contracts or beats every minute (Kenny et al. 2015). A resting heart rate is typically between 50-90 bpm (beats per minute) (Fahey et al., 2020). When the heart rate is less than 60 bpm, the term used to describe this is bradycardia (Kenny et al., 2015). Sometimes, bradycardia is cause for concern, but it can also be a result of someone who has a high level of cardiovascular fitness. The term tachycardia is given to heart rates above 100 bpm. While a high resting heart rate can be caused by various pathological reasons, heart rate may also be elevated during exercise (Kenny et al., 2015) or even in high-stress/ emotional situations.

Blood Pressure

The term blood pressure is likely one you have heard before. Blood pressure is the pressure put on the blood vessels by the blood traveling through them (Kenny et al., 2015). This pressure is caused by the pumping action of the heart (Fahey et al., 2020). If we think of the heart as a pump, it makes sense that the pressure would be greatest in the blood vessels closest to the heart and decrease the further away the vessels are from the heart. Typically blood pressure is measured in the brachial artery (located in the arm). The standards you have likely heard of related to blood pressure are specific to the pressure in this artery.

Blood pressure is expressed as two numbers, systolic/ diastolic. The systolic (top number) is the pressure during ventricular (lower heart chambers) contraction, and the diastolic is the pressure during ventricular relaxation (Kenny et al. 2015). The link below includes the systolic and diastolic recommendations for adults recommended by the American Heart Association.

Understanding Blood Pressure Readings

Blood pressure that is too high (hypertension) increases the risk of having a cardiovascular event such as a heart attack or a stroke (Fahey et al., 2020). For people with blood pressure that is on the high side of the normal range, physical activity, weight management, and nutritional changes can aid in preventing blood pressure from getting to a hypertensive level. With that said, it is important to listen to a physician’s recommendations regarding blood pressure management (often medication is prescribed), and what physical activity is safe for individuals with hypertension.

Changes To The Cardiovascular System With Exercise

At rest, the cardiovascular system functions at a mostly steady pace. For example, healthy individuals typically have a resting heart rate (RHR) between 60 and 80 bpm (Kenny et al., 2015) and breathing rates of about 15 breaths per minute (Breathe, 2020). Additionally, only about 15-20% of blood leaving the heart goes to the working muscles. During exercise, the demand placed on the cardiovascular system increases in order to deliver more oxygen to working muscles (Kenny et al., 2015). In order to meet the increased demand for cardiovascular activity or exercise, HR will increase.

Additionally, the heart will send out more blood with each contraction. The term used for the amount of blood leaving the heart every contraction (beat) is stroke volume (Kenny et al., 2015). So the heart is not only contracting more each minute, but with each contraction, more blood is leaving the heart. There are also changes in blood flow patterns. We dramatically increase the amount of blood being sent to the working muscles. During maximal exercise, 80-85% of blood goes to the working muscles.

Regarding breathing rate, we can increase our breaths per minute. Breathing rate can increase up to 40-60 breaths per minute (Breathe, 2020). In addition, with each breath, we also bring in a great volume of air! Systolic blood pressure also increases during an exercise bout (Kenny et al., 2015).

Why Is Cardiovascular Endurance Important?

Take a moment and think about why cardiovascular endurance is important. Brainstorm some reasons.

You may wonder what happens to an individual who is inactive and has a very low level of cardiovascular endurance. If this is the case, as time goes on, even low-level activity can become challenging and become work for the body. Often, in these cases, the individual with low cardiovascular fitness starts to do even less. They may stop taking stairs and only use elevators, or they may spend as little time moving as possible. It becomes a downward spiral– as fitness decreases, the person does less, and fitness decreases more. What happens if this individual needs to be physically active? What if they need to remove snow from their car or chase after a pet that got loose. These narratives are all too common, but they do not need to be the narrative! If someone’s cardiovascular fitness is lower than they would like, there are things they can do to improve it!

 Exercise that maintains or improves cardiovascular endurance is called aerobic exercise (exercise that requires oxygen). Participating in aerobic activities decreases the chance of premature death from all causes, but primarily cardiovascular disease (ACSM, 2013).

As mentioned in Chapter 3, The ACSM (2013) recommends that adults between the ages of 18-65 who are healthy participate at a minimum of 150 min (30 min/five times a week) of moderate-intensity aerobic exercise (exercise that raises your heart rate and breathing rate) or participate in 60 min (20 min/ 3 times a week) of vigorous exercise. In Chapter 3, we also talked about what vigorous vs moderate intensity means. Moderate intensity cardiovascular exercise raises heart rate to roughly 64 – <76% of your Max HR (ACSM, 2018).

Measuring Aerobic Exercise Intensity

As mentioned above, a common way to determine your cardiovascular exercise intensity is to determine the percentage of your maximal HR that you are working at. Below are two ways in which to determine your Target HR zone. One being the Traditional Method and the other being the Karvonen Method.

Traditional Method of Determining Target HR Zone

Take a moment and determine your age predicted maximal heart rate:

220 – age = predicted HRmax

220 –         =        bpm

The above equation estimates HR max. This equation is easy to complete and gives most people a good estimate of their maximal HR (ACSM, 2013). Once you have your Max HR you can then multiply that number by a percentage to determine your target HR range. For example if you are looking to exercise at a moderate intensity, you would likely be looking to exercise between 64– <76% of your Max HR (ACSM, 2018).

Note: Remember that this is an estimation! To get your actual HR max, you would need to complete something called a graded exercise test (every few minutes, often times every 3 minutes, the cardiovascular demand of the exercise gets harder) to maximal exertion. A maximum graded exercise test is designed to eventually get you to a point where even when you increased the exercise intensity/ cardiovascular demand, HR would not increase. This would yield someone’s true HR max! This test can be time consuming, potentially unsafe for some people, and oftentimes people stop the exercise before they reach a true HR max (thus not giving the needed information).

220 – age = predicted hr max

Below is the Karvonen method of estimating Target HR. In order to complete this method, you need to determine your resting heart rate. One way to do this is to take your pulse! Many wearable devices can also give you this information.

Taking your pulse: In order to take your pulse, you first need to locate it! The easiest location to do this is via the radial artery, located on the thumb side of your wrist, or the carotid artery, located in your neck. The video below can help you locate both your radial and carotid pulses. When taking your pulse, you should use your index and middle finger (first two fingers after your thumb). you could count your pulse for an entire minute to get your bpm (beats per minute), or you can count a 10-second pulse and multiply it by 6!

Karvonen Method of Determining Target HR Zone

The Karvonen method of determining target heart rate differs because it takes Heart Rate Reserve (HRR) into consideration (HRmax – HRrest) (Kenny et al., 2015). Resting HR is typically lower in individuals who are more cardiovascularly fit. So the benefit of this method is that it takes more than just age into account. It also takes cardiovascular fitness into consideration. To get your true resting HR, you would want to take your pulse first thing in the morning. If that is not possible, you should, at the very least, sit and rest for 5 min before taking your pulse (Your resting pulse may be altered by recent activity, stress, or caffeine).

Note: The above examples are for a 20-year-old with a resting pulse of 60 bpm.

Another simple way to estimate your cardiovascular exercise intensity is the Talk Test. If you are participating in cardiovascular exercise at an intensity that allows you to talk conversationally but not sing (you would be too out of breath), you are likely working at moderate intensity. According to Fahey et al., (2020), if you could not talk conversationally, as you would be too short of breath, you are likely working at a vigorous intensity.

Measuring Cardiovascular Endurance

As you may recall from Chapter 3, cardiovascular endurance is one of the health related components of fitness. This means that individuals need to have a threshold level of cardiovascular endurance for health. The gold standard to measure cardiovascular endurance is a VO2max test (Kenny et al., 2015). The VO2 max test assesses one’s max aerobic or cardiovascular capacity. In other words, the maximal amount of oxygen an individual is capable of consuming at max cardiovascular exercise. A true VO2max test yields the most accurate results, but for many reasons, it is often not possible. In order to conduct a true VO2max test one needs access to a metabolic cart, as well as someone capable of running the test. Additionally, oftentimes less cardiovascular fit individuals will end the test prior to reaching a true VO2max and thus not yielding accurate results. Because it is not always safe or practical to conduct a true VO2max test, there are other valid and reliable tests to measure cardiovascular endurance.