Defining Sedentary Behavior and Its Potential Health Risks

Defining Sedentary Behavior

Defining Sedentary Behavior and Its Potential Health Risks

Building healthier habits can be challenging. Making smart food choices and dedicating yourself to exercise are great places to start in your everyday routine, but another factor may be affecting your health just as much—sedentary behavior. While many are calling sitting the new smoking, there is still too little objective data to support this dramatic conclusion. Here is what we do know about this very common behavior.

What is sedentary behavior?

In early studies which measured how often people engaged in sedentary behavior, sedentary behavior was defined as any waking behavior or activity that involved energy expenditure of 1.0 to 1.5 METS.

1.0 MET = the amount of energy it takes to just sit quietly

Example, playing handball for 10 minutes = 12.0 METS because it requires 12 times as much energy as just sitting still for 10 minutes

The Compendium of Physical Activities (2011) lists the METS energy expenditure for hundreds of different activities.

In the last decade or more, our sedentary behavior has become much more likely to involve “screen time” (watching television, using the computer or a smart phone); so the definition of sedentary behavior has evolved to include activities done while sitting or in reclining posture which require an energy expenditure less than 1.5 METS. Studies have shown individuals can spend more than half of their waking hours in sedentary activities.

What do early studies show about sedentary/sitting behavior and health risks?

Early studies have demonstrated that increasing sedentary behavior is associated with increasing risk of death from heart disease or any cause. In these studies, sedentary behavior was assessed using self-report (people filled out a questionnaire about sitting time at work and at home). More recent studies have been harnessing the power of technology to measure sedentary time using gadgets that measure activity in the upper body and lower body and moving forward and backward and up and down.

Because this is a developing science, American Heart Association published a recent scientific advisory that recognized the important findings of these initial studies but suggested further research is needed among diverse groups in order to make public health recommendations: in men and women, old and young, diverse ethnic and racial groups and across levels of BMI, fitness, burden of chronic disease and more.

That being said, because of what we know about the adverse effects of prolonged sitting on blood sugar levels, we expect these more objective assessments of sitting time and outcomes will demonstrate that sitting does increase health risks in many people.

Why could prolonged sitting have an adverse effect on health?

There is accumulating information about the adverse effect of sitting on blood sugar metabolism. When we eat, our digested food increases the sugar (glucose) level in our blood and the pancreas releases a hormone called insulin which helps get sugar out of the blood stream and into the body’s tissues and organs to make energy.

The organ in our body that uses a lot of the sugar in our bloodstream for fuel is our skeletal muscle. Movement of sugar out of the blood stream into the skeletal muscle is stimulated by insulin and also by muscle contraction. When you are standing or moving, your skeletal muscles contract to keep you from collapsing on the ground as well as propel you forward. This helps get blood sugar out of the bloodstream and into your muscles, thus lowering blood sugar.

If we become overweight or obese, our bodies become resistant to the actions of insulin, making it harder to get the sugar out of the blood stream into the skeletal muscles. As we become more sedentary and contract our muscles less, the very same thing occurs. Combine weight gain and increased sitting time, and you set the stage for the development of pre-diabetes or diabetes. Not surprisingly, there are many studies that demonstrate regular physical exercise can delay or prevent the onset of diabetes.

Sitting vs. Standing

Identifying strategies to reduce sitting time is a huge focus of research and in turn, commercialization! The standing desk is one of the most popular trends appearing in offices around the country.

Standing desks do result in the need to contract muscles to remain standing which is a good thing. However, work-related standing activities associated with energy expenditures are not much higher than typical sedentary activity:

Standing while copying documents (1.5 METS)

Standing while talking in person or on the phone, working on the computer or text messaging with light effort (1.8 METS)

Drawing, writing or painting when standing (1.8 METS)

Standing while filing and assembling (2.3 METS)

While some internet stories suggest standing burns 50 calories per hour, rigorous studies where energy expenditure (oxygen consumption) is actually measured during standing and sitting demonstrate the calorie burn from standing is about eight extra calories per hour. However, moving around for 30 minutes burns 110 calories!

So far, studies of the use of sit-stand desks have been with small numbers of participants over short periods of time. These studies have not demonstrated significant health benefits with trading standing for sitting but they have demonstrated that there has not been an increased risk of musculoskeletal injuries or reduced work performance. So, if you love your standing desk because it reduces your back pain and keeps you alert, terrific. If you hate your standing desk because your back hurts and you have trouble focusing on complicated tasks, get rid of it!

What is the best approach for combating the potential health risks of sedentary/sitting behavior?It is safe to say physical activity will give you more bang for your buck then just standing. What we don’t know is the most beneficial dosing during the day. Should you walk for five minutes every hour? Walk for 30 minutes three times during the day? Jog in place as fast as you can for one minute every 30 minutes? No one knows for sure. Those studies are ongoing.

In the meantime, if you work at a desk job, try these recommendations to get up and move throughout the day.

Take the stairs instead of the elevator

Get up once an hour and walk in place or around the office

If you can, take your phone calls standing up and moving around

Rather than emailing a colleague who works down the hall, walk down the hall to speak to him/her instead

At lunch, work in some physical activity during the break

If you’re inclined to sit on the couch after a long day, concentrate on spending some of that time being more active, even through simple movements such as getting off the couch to change the channel instead of using the remote, walking in place and stretching. The more you move, the better!

Article provided by Nina Radford, MD, Cooper Clinic Director of Clinical Research and Cardiologist

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