Punctual Benefits of Physical Exercise with an Emphasis on the Immune System
- Jan 26, 2022
- 6 min read
Updated: Feb 3, 2022
By Jorge A Cevallos, MD
26/01/2022
HIGHLIGHT OUTLINE
Lower incidence, intensity and mortality secondary to viral infections.
Increased pumping of blood brought on by cardiovascular aerobic exercise promotes the mobilization and redistribution of effector lymphocytes. Sub-types of lymphocytes migrate into lymphoid tissues and organs (upper respiratory tract, lungs, intestines) from reservoirs (blood vessels, spleen, and bone marrow) for increased pathogen recognition and elimination.
Regular exercise increases lymphocytes, NK cells (Natural Killer cells; key cells for anti-tumoral activity), immature B cells, and monocytes to increased levels in the blood.
Reduced damage from oxidative stress and slow-down of immune system aging.
Immune system modulation through cell-signaling molecules known as cytokines; which depending on their profile, can either increase inflammation or decrease it.
The type and intensity of exercise associated with improved cellular immunity is moderate in its intensity.
Surprisingly, high-intensity physical activity without appropriate rest can trigger decreased cellular immunity. Beyond the threshold of 90 min of moderate- to high-intensity physical activity, immune function decreases temporarily.
Superoxide dismutase -an important antioxidant in the body (highly present in the lungs)- is enhanced by resistance exercise.
The volume of contractile muscle mass involved, the duration of the physical activity, and the intensity of exercise is proportional to the increase of anti- and pro-inflammatory cytokines released by muscle contraction.
With regular physical activity, pro-inflammatory responses and stress hormones (e.g. cortisol) are decreased.
Long-term training in aerobic exercise is associated with decreased clotting potential, which in turn suggests reduced risk of ischemic events and infarction.
Reduced chronic disease risk (cardiovascular, diabetes, cancer, hypertension, obesity, depression, and osteoporosis) and reduced risk for premature death.
Increased energy expenditure, offsetting a high caloric diet.
HOW?
The release of calcium (Ca 2+) secondary to muscle fiber contraction induces the production of Tumor Necrosis Factor Alpha (TNF-α (primarily)), Interleukin-1β (IL-1β), and IL-6: pro-inflammatory cytokines.
These; among being involved in other effects, promote the synthesis of selectins – “hooks” in the inside of blood vessels - that attract neutrophils (of the first immune cells to be activated and arrive) to the site.
Later on in the response secondary to muscle contraction, elevation of anti-inflammatory cytokines such as IL-10 promote an anti-inflammatory profile with the objective to limit tissue and muscle damage.
IL-10 is also associated with enhanced insulin sensitivity and glucose metabolism.
Exercise reduces the expression of the pro-inflammatory adipokine (signaling molecule released by adipocytes (fat cells)) leptin.
HOW MUCH?
The World Health Organization recommends 150 minutes per week of physical exercise for adults, and 300 minutes per week for children and adolescents.
These recommended minutes per week can be divided throughout the week.
Do follow the regulations and guidelines on your area to comply with pandemic guidelines and public health measures.
Main Article
We often hear from friends and colleagues about how wonderful and beneficial exercise is for us ,we may even know it is good for us deep inside; yet, do we really know the benefits of exercise beyond a simple notion of what they might be?
To push further than the superficial notion of the benefits exercise provides, this will be a first in a series of posts whose goal is to dive deeper into the punctual benefits of physical activity, explore , and then describe what makes up a healthy exercise regime based on the latest evidence.
What are the broad benefits of exercise? For starters, physical activity has been shown to reduce the risk of several chronic diseases (cardiovascular, diabetes, cancer (colon, breast), hypertension, obesity, depression, and osteoporosis) and premature death (1). Furthermore, exercise reduces oxidative stress (we will have a post on this topic) and slows the aging of the immune system (2).
Some of the more punctual benefits include the following: reduction in the fat stores of adipose tissue, increased energy expenditure offsetting a high caloric diet, activity-related changes in sex hormone levels, immune function, increasesd sensitivity to insulin and insulin-growth factors, reduction of free-radicals, and anti-tumor effects (1).
It is particularly interesting to review the role of exercise on the immune system given our current state of pandemic. To start off, physical activity acts as an immune system modulator. How does it do this? It modulates the immune system through cell-signaling molecules known as cytokines. These signaling molecules can either induce inflammation or decrease it. These molecules are known as pro- and anti-inflammatory cytokines, respectively (2).
Through these molecules, exercise increases circulation and recruitment of key immune cells known as lymphocytes, which are important effectors and regulators of inflammation and infection (2). This in turn partly explains why the incidence, intensity and mortality secondary to viral infections is lower in people who exercise regularly (2). A particular signaling molecule, IFN-I, initiates the response to a viral infection by increasing the action of macrophages and lymphocytes. It is interesting to note that a suppression of IFN-I has been noted in COVID-19 (2).
Does every type of exercise exhibit the same benefits? No, the type and intensity of exercise associated with improved cellular immunity is moderate in its intensity. Surprisingly, high-intensity physical activity without appropriate rest can trigger decreased cellular immunity; hereby increasing the propensity to infection (2). The observed decrease in immune function has been observed to occur at the threshold of 90 min of moderate- to high-intensity physical activity (2).
How does exercise start this chain of events with signaling molecules? Well, muscle contraction initially increases the synthesis of IL-6, an inflammatory cytokine, in proportion to the duration of physical activity and the amount of muscle mass recruited (2). Later on in the response, elevation of anti-inflammatory cytokines such as IL-10 promotes an anti-inflammatory profile with the objective to limit tissue and muscle damage (2). This latter cytokine is also associated with enhanced insulin sensitivity and glucose metabolism. Furthermore, exercise reduces the expression of the pro-inflammatory adipokine - a signaling molecule released by adipocytes (fat cells) - leptin (2).
The anti-inflammatory response can be described as a Th2 cytokine profile, which is the primary profile that mediates a reduction in muscle tissue damage and has anti-viral effects. Strenuous activities, as we previously described, however, can result in immunosuppression (2).
Other interesting molecules that are up-regulated include the enzyme known as superoxide dismutase -an important antioxidant in the body (highly present in the lungs)- is enhanced by resistance exercise (2).
Subsequently, long-term training in aerobic exercise is associated with decreased clotting potential, which in turn suggests reduced risk of ischemic events and infarction. This too is proportional to the intensity and duration of exercise (2).
Hereby, it is important to re-capitulate that the volume of contractile muscle mass involved, the duration of the physical activity, and the intensity of exercise is proportional to the increase of anti- and pro-inflammatory cytokines released by muscle contraction (2).
But how exactly does muscle contraction cause the release of cytokines? This occurs when the release of calcium (Ca 2+) secondary to muscle fiber contraction induces the production of TNF-α (primarily) and IL-1β, pro-inflammatory cytokines. These; in turn, promote the synthesis of selectins – “hooks” in the inside of blood vessels - that attract neutrophils to the site (2). Additionally, under the influence of cortisol, the bone marrow releases neutrophils, and this is the reason behind exercise-induced neutrophilia, or high levels of neutrophils in the blood (2).
With regular physical activity, inflammatory responses and stress hormones are decreased (2). Also with regular exercise, lymphocytes, NK cells (Natural Killer cells; key cells for anti-tumoral activity), immature B cells and monocytes are found in high levels in the blood (2). The latter can be interpreted as a boost in vigilance by the immune system, and the former, a reduction in system-wide inflammation.
The increased pumping of blood brought on by cardiovascular aerobic exercise promotes the mobilization and redistribution of effector lymphocytes. This stimulates sub-types of lymphocytes to migrate into lymphoid tissues and organs (upper respiratory tract, lungs, intestines) from reservoirs (blood vessels, spleen, and bone marrow) for increased pathogen recognition and elimination (2).
Exercise is not only a preventive health activity, but it is also a treatment for diseases with a psychological (depression, anxiety), physical, or metabolic origin. The World Health Organization recommends 150 minutes per week of physical exercise for adults, and 300 minutes per week for children and adolescents (2). These recommended minutes per week can be divided throughout the week. Stay tuned for evidence-based guidelines and tips.
References
Warburton DER, Nicol CW, Bredin SSD. Health benefits of physical activity: the evidence. CMAJ : Canadian Medical Association Journal [Internet]. 2006 Mar 14 [cited 2022 Jan 24];174(6):801. Available from: /pmc/articles/PMC1402378/
da Silveira MP, da Silva Fagundes KK, Bizuti MR, Starck É, Rossi RC, de Resende e Silva DT. Physical exercise as a tool to help the immune system against COVID-19: an integrative review of the current literature. Clinical and Experimental Medicine [Internet]. 2021 Feb 1 [cited 2022 Jan 24];21(1):1. Available from: /pmc/articles/PMC7387807/
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