One of the most important problems we currently see within industrial countries is the sedentary lifestyle. We sit too long and too often during the week, which finally may lead to functional imbalances, chronic diseases, and so on. Although the WHO postulates that an adult needs to be active for 150 minutes (moderate-intensity) or for 75 minutes (high-intensity) during a week, most of us don´t achieve these recommendations (1). And in my opinion, I really think that this duration is more than achievable. We all should surpass them! Therefore, one study shows that for additional health benefits, adults should double the suggested amount of moderate or vigorous physical activity (1). One opportunity to reach and better exceed these recommendations can be endurance training. The health benefits of endurance training were shown by many studies (1, 2, 3). That is the reason, why I want to give you an overview of endurance training, about the difference between moderate- and high-intensity endurance training, and about the health benefits. But before we look at these topics, we need to analyze what endurance actually means.
Endurance Training can be described as a repeated isotonic contraction of large skeletal groups (1). This means that you repeat a specific movement, like running or swimming, on and on for a couple of minutes till several hours. From the physiological point of view, endurance exercise is typically performed at submaximal intensity, with the main purpose of progressively moving the anaerobic threshold. To analyze this definition, we need to know what the anaerobic threshold actually is. As you see in Figure 1, with increasing work intensity your blood lactate concentration arises and high lactate, which is also called lactic acid, is bad because it leads to a pH drop in our blood.
Figure 1 Anaerobic Threshold (Source: https://strengthmatters.com/wp-content/uploads/2019/07/screenshot-2019-07-29-at-22.24.44.png, Retrieved from 03.05.2021)
The reason for the increase is, that with higher intensity, we need to get faster and more energy from our body, to maintain the performance. Therefore, mainly glucose will be metabolized, to produce ATP, our main energy metabolite. The problem with this pathway is, that the resulting pyruvate needs to be metabolized to lactate because your oxidative systems are not enough. Firstly, our bodily systems can compensate for this in the liver, heart muscle, and skeletal muscle. But when the lactate concentration reaches the anaerobic threshold (4mmol/l), our body doesn´t have any mechanisms to compensate for the further lactate increase. This point is also called the last spot where we have a lactate steady state. This means, that the produced lactate can be compensated in the body. After this point, we see an exponential increase, where we have no longer a lactate steady state. In the long run, we need to stop the performance.
Long story short, if you have a higher anaerobic threshold and so more oxidative systems, you can tolerate more lactate and so perform higher intensities.
The next part we must look at is the cardiovascular system, which is important for the supply of arterial blood (and oxygen) to the involved muscles and constant removal of metabolic waste (such as carbon dioxide and lactate) (1). As you see in Figure 2, the energy availability, which is the main factor for endurance performance, consists of the VO2max (cardiovascular system) and the anaerobic capacity which we discussed above.
Figure 2 Determinants of Endurance (Source: https://www.researchgate.net/profile/Olav-Vikmoen/publication/317277694/figure/fig1/AS:500365718425600@1496307891449/A-model-illustrating-the-interaction-of-important-determinants-for-endurance-performance.png, Retrieved from 03.05.2021)
On the one side, VO2max can be defined as oxygen delivery. This means, how much oxygen can your cardiovascular system carry to the stressed muscles. Therefore, your cardiac output, the multiplication of your heart rate and stroke volume, is the limiting factor. To maximize this cardiac output and so your VO2max, you need to increase your stroke volume because the heart rate can´t change with endurance training. So, elite runners differ from normal people because they can pump more blood with one heart stroke into the body, and so deliver more oxygen to the muscles. On the other side, the anaerobic capacity, we already discussed, depending on the mitochondrial density. So, we already know, that lactate is bad for our body and so for our performance. But if we increase our oxidative systems with endurance training, we can metabolize more pyruvate (pre-form of lactate) with oxygen in the mitochondria and so produce less lactate, and so run longer and faster. Therefore, we need to increase our mitochondrial density.
Together, the VO2max and the anaerobic threshold are the engine of our body. But we also need to look at the work economy, like body weight, anthropometries, and shoes, to increase our endurance performance. Elite runners are not without any reason thin. And we also need to train our mental endurance, which can then increase our endurance performance. But these two points mainly consist of you, and can´t be really trained. Now you know, what are endurance training and what are determinants of endurance training we need to train. So, the next step is to look at the different endurance training methods, to improve the cardiovascular system or the anaerobic capacity.
Endurance Training can be divided into HIIT (high-intensity interval training) and MICT (moderate-intensity continuous training). On the one hand, HIIT improves your VO2max, is very time-efficient, and stresses mainly carbohydrate metabolism. MICT, on the other side, improves your mitochondrial density (and so the anaerobic threshold) and stresses fat oxidation. Also, you generate a higher energy expenditure. For a more detailed endurance plan of these both methods, check out the post on Friday.
At the end of this article, after we now know, what are determinants and methods of endurance training, we need to know, if endurance training improves our health. Therefore, I listed the most common health benefits of endurance training:
Improvement of cardiovascular fitness (hypertrophy of the heart muscle, and increased stroke volume – more economic) (1, 2)
Prevention of metabolic and cardiovascular disease (e.g., diabetes type 2, a lower amount of triglyceride, …) (1, 2)
Physical Activity: therapy for mental health improvements in cognition, depression, anxiety, neurogenerative diseases (i.e., Alzheimer´s), and drug addiction (2)
Increased red blood cell mass (carries the oxygen) (1)
The positive effect of habitual exercise compared with the effects of body weight on mortality, indicating that being fit is more protective than being lean (1)
Aerobic activities: favorable metabolic and cardiovascular effects (1)
So, we see that endurance training produces a lot of health benefits. But it is important to consider, that it depends on which training method you use. So, check out the post on Friday! In addition, maybe you already notice, most of the part was written without scientific assignment. The reason for that is, that these specific topics were covered in my last semester during the module “Exercise Biology”. So, when you want more information, then use the literature below. But this should also show you, that it is always important, to cover interesting topics also additionally on your own. That means, do not believe everything that you read. I try to always cover every topic with the current scientific data and in a factual manner. But my work is not perfect. There is more information on each topic out there, as I can cover here in the article. Always remember that!
On Friday you will get an overview of the different endurance methods. See you then!
(1) Morici, G., Gruttad'Auria, C. I., Baiamonte, P., Mazzuca, E., Castrogiovanni, A., & Bonsignore, M. R. (2016). Endurance training: is it bad for you?. Breathe (Sheffield, England), 12(2), 140–147. https://doi.org/10.1183/20734735.007016
(2) Ruegsegger, G. N., & Booth, F. W. (2018). Health benefits of exercise. Cold Spring Harbor perspectives in medicine, 8(7), a029694.
(3) Su, L., Fu, J., Sun, S., Zhao, G., Cheng, W., Dou, C., & Quan, M. (2019). Effects of HIIT and MICT on cardiovascular risk factors in adults with overweight and/or obesity: A meta-analysis. PLoS One, 14(1), e0210644.
Jones, A. M., & Carter, H. (2000). The effect of endurance training on parameters of aerobic fitness. Sports medicine, 29(6), 373-386.
Leveritt, M., Abernethy, P. J., Barry, B. K., & Logan, P. A. (1999). Concurrent strength and endurance training. Sports medicine, 28(6), 413-427.