|Too Much Sitting is Hazardous to Your Health?
Len Kravitz, Ph.D.
For years, researchers and exercise professionals have been proclaiming the health benefits of regular cardiovascular exercise. There is strong scientific evidence that moderate- to vigorous-intensity exercise plays a significant preventative role in cardiovascular disease, type 2 diabetes, obesity and some cancers (ACSM, 2006). Presently, the science of 'sedentary behavior', also called 'inactivity physiology', is an emerging field of research in health, fitness and medicine. Sedentary behavior is a distinctive form of human behavior and should not be regarded as the endpoint of the physical activity continuum (Katzmarzyk et al., 2009). In fact, adults and children in the U.S. spend the majority of their non-exercising waking day in some form of sedentary behavior such as riding in a car, working at a desk, eating a meal at a table, playing video games, working on a computer and watching television (Owen et al., 2009; Katzmarzyk et al., 2009). This article will review some of the current findings and detrimental health effects of a sedentary lifestyle.
The Deleterious Effects of Too Much Sitting
The phrase sedentary behavior comes from the Latin word 'sedere', meaning, to sit (Owen et al., 2009). Most individuals can sit for many hours at a time, day after day. In fact, approximately 70% of the waking day (of this physically active person) may be in a sitting behavior.
The initial findings of the hazardous effects of sitting behavior actually had its early research roots in the 1950s, when researchers showed that men in physically active jobs have less coronary artery disease during middle-age, and what disease they have is less severe, and they develop it later in life than men in physically inactive jobs (Morris & Crawford, 1958). Leaping forward half a century, in a recent large follow-up prospective study (looking at mortality over a 12-year period of the 7,278 men and 9,735 women, 18 to 90 years of age; mean age = 42 yr) from the Canadian Fitness Survey, Katzmarzyk et al. (2009) summarize that there were 759 deaths from cardiovascular disease, 547 deaths from cancer and 526 deaths from other (e.g., respiratory diseases, injuries, violence, mental disease, nervous system illnesses and digestive system disorders). After adjusting the data for potential cofounders (e.g., adjustments for age, sex, smoking status, alcohol consumption, leisure time and physical activity), the authors highlight that even with physically active individuals, there is a strong association between sitting and mortality risk from all causes including cardiovascular disease. Thus an important finding from the Katzmarzyk study is that physical activity does not cancel out the ill effects of too much sitting. This is true even if the person meets the current minimum physical activity guidelines (ACSM, 2006) of moderate intensity exercise for 30 minutes/day on most days of the week. The highest mortality sub-population group is obese men and women who spend most of their waking time sitting.
What are the Physiological Mechanisms to Sedentary Behavior?
Although the preponderance of investigations on the physiology of sedentary behavior versus light physical activity versus moderate- to vigorous-intensity exercise have been completed with animal models, new insights in explaining this unique behavior are surfacing. Hamilton et al. (2008) explain that when rats are not allowed to stand, there is a very dramatic drop in the enzyme (lipoprotein lipase) in the leg muscles that captures fat (triglyceride) out of the blood to be used by the body for fuel. Thus, with consistent sitting, blood triglyceride levels start to soar higher, elevating the risk for cardiovascular disease (CVD). This same physiological phenomenon is what is hypothesized to happen in humans. As well, Hamilton and colleagues note that a clinically relevant decrease in the HDL cholesterol (the good type) is also observed with these long periods of sitting (on a daily basis). Therefore, this early research shows that sedentary behavior appears to have a significant affect on some the main contributing factors of CVD. Hamilton and associates explain that this preliminary sedentary behavior physiology research supports the 'specificity of training' principle, stating that the body will adapt specifically and uniquely to the demands (or lack of physical demands) placed upon it. Katzmarzyk and colleagues (2009) underscore that the evidence indicates that the physiological mechanisms related with extensive sitting are different than the physiological benefits associated with consistent cardiovascular exercise.
A New Approach for Fitness Professionals
For decades, exercise professionals have been emphasizing the need for structured exercise as the guiding tenant of the physical activity and exercise program design. It is now clear that too much sitting is hazardous to one's health, regardless if the person meets the minimal daily exercise guidelines. Hamilton et al. (2008) suggest fitness and health professionals need to consider recommending, IN ADDITION to existing program design guidelines, innovative approaches to reducing sedentary behavior.
Practical Application 1) One way for exercise professionals to approach this first recommendation is to develop a 'waking day metabolic profile timeline' (or energy expenditure profile) for each client or student.This waking day timeline will serve as an awareness index for the client to realize how much sitting he/she is doing on a daily basis. Hamilton and colleagues continue that the next step is to find ways to sit less and stand more throughout the day, particularly during sustained periods of sitting. This brings forth the concept of incorporating frequent episodes of spontaneous physical activity throughout sustained sitting times of a person's 'metabolic profile.' The most notable spontaneous physical activity research has been pioneered by James Levine, M.D., Ph.D. (See IFJ (2006), Volume 3(4), pp. 24-25) who calls this type of energy expenditure non-exercise activity thermogenesis (NEAT). Levine encourages all individuals to add activity to their daily life wherever and whenever possible. So, once the exercise professional has a clear metabolic profile for the client, working together to incorporate bouts of spontaneous physical activity during sustained periods of sitting is the next objective.
Practical Application 2) To complete this second objective, let's do a case study of a client who's metabolic profile shows he/she works (M-F) at a desktop computer work station for 4 hours in the morning, 4 hours in the afternoon and watches TV and reads for 2 hours each night.
Some (but not all) spontaneous physical activity options to discuss to break-up these sustained sitting periods at work might include:
1) Stand up and walk around the office every 30 minutes
2) Stand up and move every time the person needs to get some water
3) Walk to the farthest bathroom in the worksite facility when going to the restroom (if multiple bathrooms are an option)
4) Always stand and/or walk around room when talking on the telephone
5) Consider getting a standing workstation where the client can stand and work on the computer (most of these work desks can be raised and lowered so if the user becomes fatigued from too much standing there is an option to lower and sit in a chair or on a physioball to continue work)
6) Consider doing a 5-minute walk break with every coffee break
7) Don't email office colleagues; walk to their desks to communicate with them
For the 2-hour time frame of watching TV and reading consider some of the following spontaneous physical activity options:
1) Get up and move during every commercial
2) Take a 5-minute walk break every 30 minutes
3) Get a stationary piece of cardiovascular exercise equipment and use it for several minutes each half-hour of TV viewing or reading
4) Stand up and do some easy (i.e., not strenuous) lunges or squats at least once per half hour
5) Stand up and do some alternating leg balance exercises at least once per half hour
6) Stand up and move for the opening segment of each TV show
7) At the end of reading every 4, 6 or 8 pages get up to walk around the room or house
The information and research presented above suggests that sedentary behavior can be very harmful to one's health. Fitness professionals need to address this issue with creative and novel strategies to help clients stand up and move during sustained sitting periods of the day. We can do it!
ACSM. (2006). ACSM's Guidelines for Exercise Testing and Prescription (7th ed.). Philadelphia: Lippincott Williams & Wilkins.
Hamilton, M.T., Healy, G.N., Dunstan, D.W., Zderic, T.W., and Owen, N.O. (2008). Too little exercise and too much sitting: Inactivity physiology and the need for new recommendations on sedentary behavior. Current Cardiovascular Risk Reports, 2, 292-298.
Katzmarzyk, P.T., Church, T.S., Craig, C.L., and Bouchard, C. (2009). Sitting time and mortality from all causes, cardiovascular disease, and cancer. Medicine & Science in Sports & Exercise, 41(5), pp. 998-1005.
Morris, J.N. and Crawford, M.D. (1958). Coronary heart disease and physical activity of work: Evidence of a national necropsy survey. British Medical Journal, December 20, pp. 1486-1496.
Owen, N., Bauman, A. and Brown, W. (2009). Too much sitting: a novel and important predictor of chronic disease risk? British Journal of Sports Medicine, 43(2), pp. 81-83.