Muscle Up Your Immune System
Skeletal muscles, such as biceps and quadriceps, are those that enable movement, for example, hitting a tennis ball, riding a bike, or simply opening a door. But as researchers have discovered, skeletal muscles are responsible for much more than locomotion.
The field of investigation known as “exercise immunology” is fairly new, emerging some 20 years ago. Studies have shown that flexing skeletal muscles stimulates molecules that commune with immune cells throughout the body.
“The immune system especially benefits from cardiovascular exercise that utilizes whole-body, large muscle groups by releasing white blood cells (WBC) into circulation between the blood and tissues for constant monitoring for antigens,” explains exercise physiologist Daniel Hernandez, MS, UCLA Cardiac Rehab Center. “Specifically, neutrophil concentrations, which are considered the first responders to microbial infections, increase during and after exercise.”
According to the American College of Sports Medicine, WBC concentrations can increase within the first 10 minutes of aerobic and resistance exercise.
The Goldilocks Principle
When it comes to exercise and the immune system, it’s about not too much, not too little, but just the right amount of physical activity. Of course, “right” is a relative term. What’s right for someone who has been running daily for most of her life is different compared to someone who has spent a lot more time on the couch. Exercise physiologists and personal trainers refer to physical intensity in terms of VO2 max, which is a measurement of the maximum amount of oxygen used during movement. VO2 max testing is typically done in a sports lab and involves a complicated equation calculated in milliliters of oxygen consumed in one minute per kilogram of body weight.
There is an easier way to determine moderate effort, though it is not as precise.
“Casual and experienced exercisers can gauge their exercise intensity by either monitoring heart rate (HR), typically by using a Fitbit, Apple watch, or another smartwatch device, or by using ratings of perceived exertion (RPE),” says Hernandez. “RPE is a subjective scale based on how hard people think they are exercising, taking into consideration breathing rate and how muscles feel. The RPE uses a rating between 6 and 20, where a rating of 6 is none to very light work, and a rating of 20 is vigorous/very hard exercise.”
Moderate is where you want to be for bolstering immune function. A study that compared elite triathletes to recreational triathletes found that the elite athletes were twice as likely to become ill compared to recreational athletes. Broadly speaking, heavy training is defined as more than two hours of intense physical activity most days of the week. Elite athletes who train and participate in competitions are also at risk because of potential exposure to pathogens during travel, disruptions in sleep, and higher mental stresses related to competition. Risk of upper respiratory tract infections is also greater in those who engage in intensive training periods.
Elite athletes are of course the exception in society. The truth is most people don’t get enough physical activity. Once the sixth and seventh decades in life are reached, it becomes ever more important to develop or maintain a physically-active lifestyle. You don’t have to run a marathon, but you do need a dedicated exercise plan that gets your body moving and your heart rate up most days of the week.
“Immune cells are constantly circulating during moderate-intensity exercise, enabling us to be more resistant to infection,” explains Hernandez. “Contracting skeletal muscle also releases cytokines that help with immunity, such as interleukin 6 (IL-6), IL-7, and IL-15. IL-6 has pro- and anti-inflammatory properties, assists in repairing muscle damage, and can direct immune cells to areas of infection. IL-7 and IL-15 help produce and maintain other WBC, which all help to fight against potential infection.”
Lowering Inflammation
According to a review study published in the May 2019 issue of the Journal of Sport and Health Science, when repeated on a regular basis, moderate exercise confers multiple benefits, including decreased incidences of illness and dampened systemic inflammation. A “review study” bases findings on numerous existing studies with defined parameters for inclusion. In this case, the review analyzed 179 studies and consolidated the findings in the publication.
One of the studies analyzed included 1,000 adults ages 18 to 85; 60 percent female and 40 percent male. Two groups (sedentary people versus exercisers) were compared over a 12-week period. The exercise group engaged in at least 20 minutes of aerobic exercise, on average five days per week. The researchers found that exercise frequency was associated with reduced number of days with upper respiratory tract infections (URTI). The number of days with URTI was 43 percent lower in those who exercised at least five days per week. Despite the fact that intense exercise bouts can increase some inflammatory compounds immediately after exercise, there is evidence that exercise decreases overall inflammation in the body. Also, physically fit people have lower levels of inflammatory biomarkers when they are at rest compared to people who are obese and unfit. Persistent, or chronic, inflammation is linked with many disorders, including arthritis, atherosclerosis, cardiovascular disease, kidney disease, type 2 diabetes, obesity, osteoporosis, dementia, depression, and some cancers.
Counteracting Age-Related Immune Changes
Everything changes with age, some for the good, some not so much. Many people become wiser and more patient with age. The immune system, however, is known to be less efficient through time. The term “immune senescence” refers to the age-related decline of the immune system, which results in increased susceptibility to infections, diseases, and neurologic disorders. Healing also takes more time. It doesn’t necessarily have to be a steady downward decline. Studies have shown that even later in life, you can influence how your immune system responds to challenges. Exercise is a significant contributor. A study that compared 30 sedentary elderly women to highly conditioned elderly women who made choices such as participating in state and national senior games and endurance races showed that the conditioned women had higher levels of natural killer cells and better T-lymphocyte (T cells) function. T cells are major immune system players. The conditioned women also showed reduced rates of illness compared to their sedentary counterparts.
In addition, data shows that a regular exercise habit can improve vaccination response, lower circulatory levels of inflammatory cells, and lengthen telomere (the end caps of DNA which, when shortened, accelerate age-related demise).
On the flip side, people with sarcopenia (age-related loss of muscle strength) take longer to heal after infections and surgery. People with severely weakened muscle have double the risk for infection after surgery.
But all is not lost even if you haven’t seen the inside of a gym for a very long time. Positive immune responses from exercise occur within a single session, though for sustained improvement, you need to be active most days a week. Make it a goal to exercise a minimum five days perweek doing at least 30 minutes of moderate intensity aerobic exercise (walking, biking, etc.).
“If you are just starting out, try two to three 10 to15 minute walks throughout the day, and gradually build the walking duration until reaching 30 minutes,” recommends Hernandez. “Of course, take breaks as needed.”
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