Endurance Exercise
Endurance Exercise
Endurance exercise is often referred to as aerobic exercise in scientific literature, in common place it's referred to as cardio. Throughout this blog post, I am going to refer to cardio as both, endurance and aerobic exercise. It's important to understand that the generalized term aerobic refers to any mode of exercise that requires oxygen to create energy. While this blog could take a deep dive into glycolysis, Kreb's cycle and the electron transport chain, I would rather take the time to discuss the benefits of aerobic exercise and how to properly design an aerobic exercise program. For those studious readers looking to refresh their memory on physiology, I've included a link for both glycolysis, Kreb's Cycle and the electron transport chain. Without further avail, let's dive into endurance training!
Exercise
At the onset of exercise, the body perceives exercise as a threat and turns down the parasympathetic nervous system (PNS - rest & digest) places more demand on sympathetic nervous system(SNS - fight, flight, or freeze). As a result of increased SNS activation due to the release of catecholamines such as epinephrine and norepinephrine the body will respond in a number of ways. The most common responses are increasing heart rate (HR), respiration rate (RR), stroke volume (SV), Cardiac output (Q), and blood pressure (BP). The primary objective of the body at this point is to get oxygen-rich blood to flow more quickly throughout the body. While at the same time removing carbon dioxide and other metabolic by-products as quickly as possible. Upon cessation of exercise, the body will begin to shift out of a SNS dominant state and as a result HR, RR, SV, Q, and BP will drop. If this stress only occurs minimally, 1x a week or a couple times a month, the body will have no need to adapt to the stress, and thus the benefits of regular exercise are never achieved.
Regular aerobic exercise has been demonstrated to reduce the risk of chronic diseases such as cardiovascular disease, high blood pressure, type 2 diabetes, certain cancers, osteoporosis, and improve immune system function (1 & 2).
When performing aerobic activities, there are numerous health benefits to gain. These benefits include, a reduction in resting HR (RHR) and reduction of both systolic and diastolic blood pressure.
Aerobic Capacity
I believe one of the most noticeable adaptations to aerobic endurance training is an increase in maximal oxygen consumption and increase in Q. A basic example of this idea is: an individual started to train for a 10K - the longer they have been training the more metabolically fit they would become. If we were to measure the maximal oxygen consumption (VO2max) and lactate threshold (LT) at Day 0 and at Day 120 of following our training protocol - we would likely measure a 5-30% increase in their work capacity (depending on prior fitness level and genetics).
Frank-Starling Mechanism
Before we jump right into Frank-Starling Mechanism, let's think about an elastic band. As an elastic band stretches further and further, the more powerful the recoil becomes. Now back to the heart, the increase in work capacity was largely due to the fact that the left ventricle of the heart becomes stronger. When the left ventricle becomes stronger it's able to undergo a greater stretch and thus a more powerful recoil. This powerful recoil is able to eject more oxygen rich blood per beat. This principle is called the Frank-Starling mechanism.
As the individual continues on their training plan - there are many other physiological changes that will occur.
Exercise Economy
Exercise economy is how efficient an individual is at a task. When beginning a new sport or exercise routine, it's important to start slowly for 2 reasons:
1) Slowing down movements allows your neural pathways to learn the new skill (3)
2) Controlled movements can reduce risk of injury or re-injury (4).
As the individual progresses through the learning process the skill can be sped up. Let's use running as an example - as an athlete runs more often, their form becomes better. As a result of better form their stride length slightly decreases and frequency increases compared to those runners who are novices.
Before we discuss the components of a well-designed aerobic exercise programs let's recap what we have discussed thus far.
1) Aerobic exercise refers to any sport that utilizes oxygen
2) At the onset of exercise, the body perceives exercise as a threat and thus places more demand on the SNS (fight, flight or freeze)
3) If an individual exercises minimally - for example - 1x a week the body will have no need to adapt to the stress, and thus the benefits of regular exercise are never achieved.
4) Regular aerobic exercise has been demonstrated to reduce the risk of chronic diseases such as cardiovascular disease, high blood pressure, type 2 diabetes, certain cancers, osteoporosis, and improve immune system function.
5) Depending on fitness level and genetics - When an individual begins an aerobic exercise routine multiple times a week for a few months. It is typically expected to have 5-30% increase in their Vo2max and/or work capacity.
How to Design An Aerobic Program
Exercise mode: Specificity of exercise is extremely important when it comes to a specific sport, for example, the individual training for 10k should use running as their primary mode of exercise. If it's the off-season, the individual is recovering from an injury, or their exercising for health; then a variety of modes would be warranted and/or non-load bearing exercise i.e. swimming.
Frequency: Frequency refers to the number of training sessions per week. Training status i.e. beginner vs. experienced individual will impact number of sessions per week. For those beginning a new routine, a common starting place is 2-3 sessions per week. For those with more experience 3 - 7 sessions per week are more common.
Intensity: Intensity refers to how much effort an individual is "giving". It's important to note that the greater the intensity, the shorter the duration and vice versa. The most common ways to measure intensity is through heart rate (HR) rating of perceived exertion or talk-test. We often recommend HR as it's the easiest to measure and is a reliable measurement. Stay tuned for a more detailed blog post on intensity and duration this fall. Where we will take a deep-dive into this topic.
Duration: As previously mentioned, the greater the duration the lower the intensity must be. If intensity is too much then metabolically speaking the body will begin to use glycolysis for energy rather than the Kreb's cycle and the electron transport chain. Ultimately, this means that the body will begin to produce metabolic by-products such as H+ ions that will cause fatigue and eventually lead to an individual halting exercise as a protective mechanism.
Progression: Too much too fast can lead to injury and decreased enjoyment of exercise. As a result typically no more than a 10% combination increase of duration, intensity and frequency is recommended (5). Generally, it is recommended that individuals always include at least one recovery or active rest day per week. Otherwise, overtraining could result.
Exercise is an environmental hormetic that stresses the body. While the word stress can carry a negative connotation, stress can be both good (eustress) and bad (distress). Exercise is a eustress, due to the fact this type of stress causes the body to adapt positively. The hormetic stressor has many benefits within the body including stronger mitochondria (6).
It's important to end this blog post with this idea, exercise is wonderful for the body. However, it is equally important to have a good quality recovery program that includes plenty of high quality sleep, nutrition and outdoor time and of course, acupuncture!
1) Warburton, D. E., Nicol, C. W., & Bredin, S. S. (2006). Health benefits of physical activity: the evidence. CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne, 174(6), 801–809. https://doi.org/10.1503/cmaj.051351
2) Campbell, J. P., & Turner, J. E. (2018). Debunking the Myth of Exercise-Induced Immune Suppression: Redefining the Impact of Exercise on Immunological Health Across the Lifespan. Frontiers in immunology, 9, 648. https://doi.org/10.3389/fimmu.2018.00648
3) Krishnan C, Dharia AK, Augenstein TE, et al. Learning new gait patterns is enhanced by specificity of training rather than progression of task difficulty. J Biomech. 2019;88:33-37. doi:10.1016/j.jbiomech.2019.03.014
4) Gokeler A, Neuhaus D, Benjaminse A, Grooms DR, Baumeister J. Principles of Motor Learning to Support Neuroplasticity After ACL Injury: Implications for Optimizing Performance and Reducing Risk of Second ACL Injury [published correction appears in Sports Med. 2019 Feb 21;:]. Sports Med. 2019;49(6):853-865. doi:10.1007/s40279-019-01058-0
5) Hagerman, PS. Aerobic endurance training program design. In NSCA's Essentials of Personal Training. 2nd ed. Coburn, JW, and Malek, MH, Eds. Champaign, IL: Human Kinetics, 389-410, 2012
6) Musci, R. V., Hamilton, K. L., & Linden, M. A. (2019). Exercise-Induced Mitohormesis for the Maintenance of Skeletal Muscle and Healthspan Extension. Sports (Basel, Switzerland), 7(7), 170. https://doi.org/10.3390/sports7070170
