Let’s get America Moving Again, Part I: How Do We Even Know Physical Activity is Good?
In my last post, I summarized my trip to Washington D.C. to lobby for physical activity. Over the next several blog posts, we will explore current issues surrounding physical activity levels in America. But first, we’ll talk about how we established physical activity is good for us.
We could discuss how exercise is beneficial for multiple organs in our body at mechanistic level , but everyone likes a good story. So, let’s start with some history.
In 1953 Dr. Jeremiah Morris, a pioneer in the field of physical activity epidemiology, published the London Transit Worker’s Study. Physical activity epidemiology is a field that involves investigating the role of physical activity in observational studies. So, essentially this entails measuring or estimating physical activity at a time point or repeatedly over time and determining frequency of disease(s) or some other variable(s) (e.g., happiness or income). Anyhow, this particular study is one of the first studies to suggest that regular physical activity is important for our cardiovascular health. Dr. Morris demonstrated that London bus drivers (a sedentary job) died more frequently of heart attacks than London bus conductors (a more active job). These findings were mirrored in other transportation workers (drivers and conductors from the trolley and train lines). Dr. Morris subsequently found that British government postal clerks died of heart attacks more frequently than postal delivery men, suggesting that the more active jobs were protective against heart attacks. This year also marks the 60-year anniversary of the publication by Dr. Morris and Dr. Margaret Crawford that sought to establish a potential mechanism (there are many) as to how physical activity is protective against heart attacks. 
In the 1958 study, Drs. Morris and Crawford worked with pathologists from around Britain to determine the extent of myocardial fibrosis (thickening of the heart, and early sign of heart disease) in men who died of causes other than heart attacks. The main finding was that men with more active jobs had fewer signs of heart disease compared to men who worked sedentary jobs.
This line of observational work has continued to grow in the time since these seminal studies. Key discoveries in this field include establishing that physical inactivity increases the risk of many of the major diseases that burden our society today, such as coronary heart disease, certain forms of cancer, and type 2 diabetes [3, 4].
Results from a more recent British publication also support the notion that daily physical activity is important for our health. In this study , researchers wanted to determine whether active commuting (walking or cycling for all or part of the journey to work and back) is an important determinant of body composition. The data was gathered from the UK Household Longitudinal Study (UKHLS). Respondents answered the question, “How do you usually get to your place of work”. Researchers categorized the responses to (a) private transport (automobile driver or passenger), (b) public transport (bus, train, rail) or (c) active transport (walking or cycling). It was assumed that public transport involved more physical activity than private based on a previous study . Think walking or cycling to and from a bus stop or train station.
Men and women who commuted via active and public transport were found to have lower body mass indexes (BMI; an index of body composition = weight divided by height). A higher number is generally worse than a lower one, but there are caveats. For example, some individuals weigh a lot relative to their height but they are very muscular, not fat. However, this study also found lower body fat percentages in active commuters compared to private transport commuters. This is important because high BMI and high body fat percentages are linked to cardiovascular disease .
Importantly, the relation between active or public transit commuting and lower BMI and body fat percentages withstood statistical adjustments that considered age, leisure exercise, and results from a questionnaire to estimate diet quality. This would suggest that independent of other lifestyle factors, a more active commute is better for our body composition. In fact, given the BMIs of the study cohort the reduced BMI in the more active commuters would translate to a body weight reduction of about six pounds. Not bad for a behavior that is just an everyday habit.
In summary, we have discussed stuides that gave helped to establish that physical activity is good for us. Admittedly, we didn’t really get into intense exercise, just physical activity as part of our daily rituals, like walking to a bus stop. We will explore the importance of building this type of physical activity into our days, in addition to regular exercise, in later posts. Until then, drop any questions or comments below and stay tuned!
Photo credit: Felix_Broennimann @ Pixabay, London bus at St. Paul’s Cathedral
Another great article on the importance of fitness and nutrition by Penn State University
Excellent write up on Dr. Morris and his pioneering work by the New York Times
Learn more about large cohort studies: Great piece by Boston University School of Public Health