ACSM’s Health & Fitness Journal

How many hours per day do you spend in sedentary behaviors such as sitting, computer surfing, texting, television watching, etc. If you are like most Americans, approximately 7.7 hours a day are spent in sedentary behaviors (¹¹), or more than half of a waking day. These hours may be relaxing but are increasingly being shown to have deleterious health effects (^4,9,10). In contrast, and in now what is becoming more and more of a distant memory, there was a time when the need for physical activity (PA) was a necessity throughout the day, especially in transportation and work. This need for PA often left little time for sedentary behaviors. However, the past 50 to 60 years have brought a noticeable shift in work, transportation, and leisure habits, leading to fewer people engaging in PA (^2,3). For example, from 1960 to 2000, there was more than a 25% increase in the percentage of adults driving to work, with 88% of U.S. adults driving daily. Similarly, from 1950 to 2000, the percentage of Americans working in high-activity occupations dropped (30% to 22%) whereas the percentage of people working in low-activity occupations rose (23% to 41%) (²). At approximately this same time, caloric expenditure from work-related PA declined by more than 140 kcal/d, or approximately 3,600 kcal/y (³)!

“Those who sit at their work and are therefore called ‘chair workers’, such as cobblers and tailors, suffer from their own particular diseases…suffer from general ill health…caused by their sedentary life.” — Bernardino Ramazzini, Italian physician, “Father” of Occupational Medicine, 1713

SEDENTARY BEHAVIOR: WHAT IT IS AND ISN’T

The definition of sedentary behavior (SED) has evolved through time, with two definitions often cited. The initial publicly accepted definition focused on intensity, stating that SED is any waking behavior or activity expending 1.5 metabolic equivalents (METs) or less (¹²). Therefore, standing, or even a very slow walk, would be classified as SED. More recently, the Sedentary Behavior Research Network (SBRN) gathered a multitude of experts to further refine the definition of SED and realized that adding a postural component to the definition would help further clarify what is and is not SED. The SBRN defines SED as “any waking behavior characterized by an energy expenditure ≤ 1.5 METs while in a sitting or reclining posture” (¹⁴). Therefore, with the current definition, SED does not include time spent sleeping, standing, or slow walking.

Sedentary behavior also is independent of physical activity, meaning an individual can be classified as both physically active (i.e., obtain the physical activity guidelines of 150 minutes of moderate- to vigorous-intensity physical activity each week) and highly sedentary, or accumulating too much SED each day. Herein lies the paradoxical active couch potato, or someone who meets PA recommendations but also accumulates a lot of SED time. Furthermore, being deemed as physically inactive only means that an individual does not meet the criteria for regular PA, yet does not necessary imply that same person is sedentary. This conundrum becomes clearer when realizing that individuals are classified as physically inactive based on PA levels and classified as sedentary based on SED levels. Because PA and SED are separate constructs, we have many individuals who embody the aforementioned active couch potato.

WHY DO WE CARE?

The idea of excessive sedentary behavior having negative health consequences has been around for a long time. In fact, data from the 1950s London Bus Drivers Study showed that middle-aged men who had to sit many more hours per week and obtain less physical activity than their counterparts had greater risk for premature myocardial infarction and mortality from coronary artery disease (⁶). In a more recent, but similar, longitudinal study, when a group of U.S. men were followed through 21 years, those who reported 10 h/wk or more sitting in automobiles had an 82% greater risk of dying from cardiovascular disease compared with men reporting less than 4 h/wk spent in a car (¹⁶). Today, the evidence of the cardiometabolic risks associated with SED only continue to mount (¹³). Self-reported high levels of SED are associated with elevated waist circumference, elevated systolic blood pressure, elevated fasting plasma glucose, elevated triglycerides, and decreased high-density lipoprotein (HDL) cholesterol, with these deleterious outcomes varying between sexes (⁹). Similarly, data collected from objectively assessed SED show that sedentary time is correlated with a greater waist circumference and unfavorable 2-hour plasma glucose and triglyceride levels (¹⁰).

BODY’S RESPONSE TO SED

Continuous periods of muscular unloading that occur during prolonged sedentary time may have detrimental biological consequences. It has been proposed that the loss of local contractile stimulation induced by sitting leads to both the suppression of skeletal muscle lipoprotein lipase (LPL) activity (which is needed for HDL production and triglyceride uptake) and diminished glucose uptake potentially leading to decreased HDL levels, increased triglyceride levels, and increased glucose levels, respectively (⁵). Further evidence suggests that SED has a direct negative influence on bone mineral content, metabolism, and vascular health (¹⁵). Breaking up sedentary time has been shown to have beneficial associations with metabolic biomarkers (i.e., body mass index, waist circumference, triglycerides, and 2-hour plasma glucose) (⁸). It has been suggested that standing, which involves isometric contraction of postural muscles, elicits electrical activity and skeletal muscle LPL changes (⁷). It is important to note that although standing may help LPL activity, it is not a replacement for daily PA and its associated health-related benefits. Thus, the focus should be on being physically active also while reducing overall sedentary time and increasing sedentary breaks.

TIPS TO REDUCE SED

Everyone should aim to replace SED with light-intensity activity whenever reasonably possible. Light-intensity activity has been shown to have an inverse relationship with a number of health biomarkers, meaning the more light activity accumulates, the better the health markers become (¹⁰). Some of the more common or typical light activities are casual walking and bicycling and light yard and housework. Some helpful tips to decrease overall sedentary time and increase sedentary breaks include:

• ACTIVE COMMUTING. If possible, consider walking or biking to your job, store, or place of worship. If that is not feasible, try parking your car further away from building entrances, maybe even a few blocks away.
• STANDING DESKS AND STANDING MEETINGS. Think about adding a standing desk option to your work environment. Similarly, try standing or walking meetings versus seated meetings.
• SET AUTOMATED REMINDERS TO MOVE. If a standing desk is not possible, you can set reminders via computer, phone, or wearable activity tracker to remind you to create hourly breaks in sedentary time. Use this time to complete a set of jumping jacks or take a quick walk around the building.
• ESTABLISH MOVEMENT CUES. Associate cues that you encounter throughout the day with movement. For example, mealtime can be a cue used to promote a movement period before eating. Or try using television commercial breaks as a cue to break up a sedentary bout by marching in place or dancing to commercial music.

CONCLUSIONS

Current research supports decreasing SED bouts and increasing SED breaks for health benefits above and beyond being physically active. Instead of SEDding ourselves up for problems,let us move more and become a SEDLESS society (SED ourseLves up for succESS).

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