Physical Activity: A Simple Approach to a Large Problem

Our great-grandparents didn’t need to exercise in order to be healthy. Many of them had jobs that involved hard physical labor.

It seems the longer the obesity epidemic plagues the United States, the more complicated solutions to this problem become.  Exercise programs become more intricate, diet plans become more extreme and hype could not be louder.  However, using an old and simplistic mindset when approaching this problem can be more effective than “the latest breakthrough in fat loss!”.  Try to recall memories of your great-grandparents.  Were your great-grandparents obese or relatively fit?  What were their daily physical activity levels?  Did they work on a farm or in a manufacturing job? If they did, their physical activity levels were probably high. But what about their exercise levels; did they even exercise at all?  I ask this because there is a difference between working on a farm all day and exercising.  Working in a farm or factory is characterized as physical activity but does not count as exercise.  Exercise is the deliberate intention of getting physical activity.  

This distinction between laboring work and sedentary work started the field of exercise physiology.  In 1952 Jerry Morris, an epidemiologist from Scotland, published a study on the differences in incidence of heart disease between sedentary bus drivers and active conductors in the London transport system.  Morris found that  both the transport conductors and drivers came from similar socio-economic status but the conductors had lower rates of heart disease.  This difference was attributed to the walking and stair climbing demanded of conductors.  Subsequent studies, co-authored by Morris, showed that not only were conductors less likely to experience heart disease, but those working jobs requiring more movement were protected from heart disease compared to their sedentary counterparts.  Although Morris recently died at the age of 99, he continues to have a positive influence on the field of exercise and epidemiology, having contributed to a study finding that meeting the minimum requirements (150 minutes/week) of exercise per week (American College of Sports Medicine and The English Department of Health) resulted in a 25% lower mortality rate compared to sedentary populations.  This means that getting just a little physical activity or exercise everyday can increase your life expectancy and quality of life.

Today, physical activity means going to a gym and running on a treadmill or elliptical.

Exercise is characterized as deliberately moving one’s body in a physically active manner with the intention of improving health and/or fitness.  I bring this up because you do not have to exercise in order to remain healthy; however, your physical activity levels need to be high.  Beyond working in a farm or factory there are other forms of applicable physical activity.  In fact, physical activity does not only have to be work, it can also be functional and fun!  Historically, physical activity is the most straightforward and most successful solution to the United States obesity epidemic.  Physical activity includes: active commuting, yard work, taking the stairs, recreational sports, dance classes and from a nomadic perspective hunting and gathering.  Active commuting involves walking or biking to work and can help solve both environmental and health problems the United States currently faces.  Active commuting has been shown to decrease chances of cardiovascular disease by 11% while also decreasing risk for cancer.

Finding a combination of functional and fun physical activity will require creativity, flexibility, and tweaking your current lifestyle but is worth it in the end.  Create a set of guidelines that will direct you towards a more physically active lifestyle.  

These guidelines should look like:

  1. Make physical activity a priority – Above anything else increasing your physical activity will require you to make mental adjustments.  Accept the fact that there may be a few inconveniences added to your life, but they are worth it.
  2. Make it simple – Stay at your kids soccer practice and walk during their practice time.  Take the stairs at work and walk to your lunch destination.  
  3. Create a social environment – Engage a friend or coworker to join you on lunch time workouts or attend evening yoga classes.  Develop friendships and camaraderie at an exercise group you join.  A study performed at Santa Clara University found that people in social exercise programs were 19% more likely to complete a weight loss exercise program and 42% more likely to maintain their weight loss.  
  4. Include a variety of activities – If you like the outdoors, find trails or paths weaving in the woods to hike or bike.  If you want to stay inside find indoor sports, dancing clubs or indoor pools.  A study at the University of Florida found that participants using an exercise plan with variety enjoyed exercise 20% more than individuals using the same plan everyday.  
  5. Stick with it – Find safe, low-cost activities and activities that can fit into your daily schedule.  Find an activity that makes you feel accomplished afterwards.

It takes leading by example and communication for ideas like this to spread, but think of the impact physical activity had on early Americans and the impact it can still have!  Challenge yourself and challenge others to jump aboard this simple solution to one of America’s largest problems.


Peer edited by Amala John.

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Exercise and Immune Response: An Overview


The relationship between exercise intensity (or volume) and susceptibility to upper respiratory tract infection (URTI) is a rotated J-shaped curve.  This means that some regular moderate physical activity decreases the relative risk of infection below that of a sedentary individual.  However, high intensity exercise or periods of much strenuous exercise can increase risk of infection. Fahlman and Engels showed a 45-50% increase in URTI prevalence in college American football players during high volume training periods. The volume of exercise needed to increase chances of URTI is usually only undertaken by higher level athletes.  

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The relationship between exercise volume and upper respiratory tract infections.

How does the immune system function?

The immune system is responsible for defending organisms against infectious bacteria, viruses and fungi (known as pathogens).  The human immune response is made of two components: the innate response and the acquired response.  The innate response is the first, non-specific wave of resistance when encountering an infectious substance for the first time.  The acquired immune response is the trained response of the immune system. This response develops after the body has come into contact with a pathogen for the first time and subsequently educates thymus immune (T) cells and bone immune (B) cells on the shape of the pathogen.  However, after the acquired response has been established, elimination of the pathogen the second time it enters the body can happen in as short a time span as a couple of hours and illness may never manifest.  

The innate response is partly composed of physical barriers such as our skin and mucous membranes.  The primary ways pathogens enter the body are though consumption (food/drink) or inhalation.  Inside the digestive tract and respiratory tract are mucous membranes that create an acidic environment hostile to pathogens.  Beyond the exterior barriers of defense, the innate immune system also has an army of cells that work together to kill pathogens. These cells work by engulfing pathogens and by communicating to other immune cells to increase activity. Lastly, the innate immune response educates T cells and B cells on the pathogen’s signature marker (antigen) so that the next time this pathogen contacts the body, the acquired immune response kicks in quickly.

Antigen pointed out on the cell surface of a pathogen

The specificity and quickness of the acquired immune response is the most critical difference between the acquired and innate responses.   The primary job of the acquired immune response is to prevent pathogens from colonizing, to keep pathogens out of the body, and to seek and destroy certain invading pathogens.  Much of what makes the acquired response so powerful are the T & B lymphocyte cells.   After encountering a pathogen for the first time, the T & B lymphocyte cells are “educated” on the proper response to the pathogen.  After a second encounter, the T & B cells quickly duplicate cells targeted at the specific pathogen.  About 90% of these lymphocytes go to attack the pathogen and communicate to other immune cells to attack while 10% stay back for future attacks.  The “memory” of the  acquired response lasts for years.   

Source: Nic Shea

Functionality of the immune system


We know now how the immune system generally works, but how does the immune system respond to exercise?

During moderate exercise, the innate response will enhance immune cell function. Conversely, during high intensity exercise, the innate response will decrease immune cell function.  Moderate intensity exercise evokes moderate levels of catecholamines (stress hormones) which may increase immune cell levels, while high intensity exercise evokes high levels of catecholamines which may decrease immune cell levels.  However, 2-3 hours after intense exercise, some immune cells are at their highest levels, which might lead to a more productive immune system as long as the exercise session did not exceed an hour.

Nic Shea

The immune response to one session of intense exercise. During exercise immune cell activity decreases. After exercise immune cell activity increases

As for the acquired immune response, it changes in proportion to the intensity and duration of the exercise session.  T cell function can increase after exercise if the session is not too long or too intense.  During long and/or intense exercise sessions, the mobility of T cells is reduced, giving pathogens a longer time to colonize before they are attacked by T cells.

The most important finding in exercise immunology is that beneficial immunological changes take place in response to moderate exercise. With each moderate session of exercise, a boost in immune system activity could reduce risk of infection. On the other end of the spectrum, trained/elite endurance athletes seemed to be more at risk to developing an infection 3 to 72 hours following a very intense session of training.  This 3 to 72 hour timeframe following intense training has been called the “open-window” theory and may be more applicable to individual elite level sporting events. When exercise sessions increase in time or intensity, aspects of an athlete’s innate and acquired immune system function will be depressed but not completely inactive.  What this means is that athletes engaging in hard periods of training are at increased risk of picking up the common cold or flu, but not at more risk of catching a serious illness.

As with nearly everything in physiology, the dose of stress or stimulus dictates the response. This seems to be the case with exercise and immune function.  A moderate amount of activity seems to be beneficial in boosting immune function, but going overboard with exercise may put you at an increased risk for infection.  However, this is mostly a concern for elite endurance athletes.  Most people would reap the benefits of increased immune function associated with increased exercise! 

Peer edited by Michelle Engle and Mimi Huang. 

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