Bushman, Barbara A. Ph.D., FACSM
Q:I MAINTAIN A RELATIVELY REGULAR EXERCISE PROGRAM INCLUDING 30 TO 40 MINUTES PER DAY OF EITHER AEROBIC EXERCISE OR RESISTANCE TRAINING BUT TEND TO BE INACTIVE IN MY “OFF” TIME, AND MY JOB INCLUDES MAINLY DESK/COMPUTER-RELATED TASKS. I’VE HEARD VARIOUS REPORTS ON THE DANGERS OF SITTING — DOES MY EXERCISE ROUTINE HELP TO OFFSET THAT? WHAT CAN I DO TO OPTIMIZE MY HEALTH?
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A:Having a regular exercise program promotes health and fitness and is encouraged for individuals of all ages (2). The benefits of regular physical activity have been clearly shown (see Box 1) (26), and regular exercise beyond activities of daily living should be included for most adults (3). A complete exercise prescription includes activities to target cardiorespiratory (aerobic) fitness, muscular fitness, flexibility, and neuromotor fitness (see Chapter 7 — “General Principles of Exercise Prescription” in ACSM’s Guidelines for Exercise Testing and Prescription, 9th edition, or the ACSM Position Stand “Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory, Musculoskeletal, and Neuromotor Fitness in Apparently Healthy Adults: Guidance for Prescribing Exercise” (3,12)). Meeting these exercise recommendations may not be enough to maximize health, however. In addition to regular exercise, reducing the amount of time spent in sedentary activities is “important for the health of physically active and inactive individuals” (3).
Sedentary behaviors seem to be encouraged as labor-saving devices and technology make even simple tasks “easier” (e.g., who remembers physically cranking down a car window, standing up to change a television station, or walking to answer a wall-mounted phone in another room of the house?). The breakdown of how people spend their time each (based on the U.S. National Health and Nutrition Examination Survey (NHANES)) was found to be as follows (17):
* Moderate to vigorous physical activity — 0.3 hours
* Light physical activity — 4.1 hours
* Sedentary — 10.2 hours
The benefits of moderate to vigorous physical activity have been widely studied, and such activity is encouraged (e.g., 3,26); see Box 2 for some of the key points from the Physical Activity Guidelines for Americans (26). Given the amount of time spent in light physical activity and sedentary behavior, researchers are focusing efforts to uncover the potential impact of these behaviors on health (see Box 3 for operational definitions of the range of behaviors and Box 4 for methods used to assess sitting time and activity levels).
As research in this area has expanded, the distinction between “too much sitting” and “too little exercise” should be considered; the latter refers to not meeting the exercise recommendations whereas the former reflects increased time spent sitting as is found with certain sedentary behaviors (e.g., television viewing, computer/game use, workplace sitting, sitting while commuting) (18). Sedentary time is associated with increased risk of diabetes, cardiovascular disease, and both cardiovascular and all-cause mortality (27). Sedentary behavior is “not simply the absence of moderate- to vigorous-intensity physical activity but rather is a unique set of behaviors with unique environmental determinants and a range of potentially unique health consequences” (18). Assuming that the volume of moderate and vigorous activities is constant, health benefits potentially increase if light-intensity activities replace sedentary activities (21). Light-intensity activities are suggested to be healthier than sedentary activities (21).
For example, the impact of sitting on all-cause death rate was examined in a large cohort of more than 123,000 individuals in a study by the American Cancer Society (20). Women who sat more (>6 hours during leisure time) had an approximately 40% higher all-cause death rate than women who sat less (<3 hours per day) and, for men, the death rate was approximately 20% higher (20). This association was found regardless of the amount of physical activity. However, when comparing those who sat more and were less physically active with those who reported sitting the least and being most active, the increases in all-cause death rates were 94% for women and 48% for men (20). Similarly, in a large multiethnic group of postmenopausal women, prolonged sitting time increased the risk of cardiovascular disease independent of leisure time physical activity (7).
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In a large cross-sectional study, total sitting time, television viewing, and leisure time computer use were associated with cardiometabolic risk factors (e.g., poorer levels of the following: body mass index, waist circumference, total cholesterol, high-density lipoprotein (HDL) cholesterol, blood pressure, nonfasting blood glucose, gamma glutamyltransferase — an indicator of liver function, and triglycerides) (4). Although causality cannot be established because the study was cross sectional (i.e., factors other than those measured could have impacted differences between individuals and the direction of the relationship cannot be determined), researchers suggest potential benefits of reducing sedentary time and limiting television viewing and computer use during leisure time (4). A recent review highlighted a significant association between screen time and cardiovascular mortality independent of physical activity (11). This is worthy of attention given that the average American spends more than 41 hours per week with screen content — including more than 34 hours of television (16).
In another cross-sectional study (NHANES), self-reported sitting time was associated with cardiometabolic health risk (as evidenced by such measures as waist circumference, triglycerides, insulin resistance, and lower HDL cholesterol, among others) (23). Researchers found differences between those who reported sitting more than 3 hours per day compared with those who reported sitting less than 3 hours per day (23). Various mechanisms by which sitting may potentially impact risk have been studied (25). Potential mechanisms include the impact of decreased muscle contraction on the uptake of triglycerides and free fatty acids, production of HDL cholesterol, uptake of glucose, and changes in energy expenditure, which could impact daily energy expenditure and weight gain (24). Other factors in specific settings also may play a role. For example, sitting while viewing television is associated with increased food consumption, which, along with lower energy expenditure, could contribute to increased waist circumference and related adverse glucose and lipid changes (18).
When considering those who engage in at least 150 minutes per week of moderate to vigorous physical activity (as recommended within guidelines from many sources, e.g., 3,26), researchers have found a detrimental dose-response association for television time and a number of health-related measures, including waist circumference, systolic blood pressure, and 2-hour plasma glucose (15). The term “active couch potato” has become attached to this phenomenon — a situation where a person achieves a recommended level of physical activity (e.g., 150 minutes per week) but is sedentary most waking hours (18). Although meeting physical activity guidelines, adverse consequences seem to be in place related to being sedentary (18).
Considering that employed adults represent about half of the world’s population and most of the population spends one third of adult life at work, the workplace is an important setting to potentially impact health by reducing sitting time and breaking up periods of prolonged sitting (1). One group of interest has been office-based workers whose occupation is sedentary. In one pilot study, researchers provided a workstation that could be transitioned between sitting and standing postures to one group of office workers (intervention group) who were compared with a group of office workers who used a typical nonadjustable work surface and who were asked to maintain their usual level of activity (comparison group) (1). The intervention group reduced sitting time (mainly because of increased standing time, although beneficial effects for transitional and stepping also were seen) (1).
Another study incorporated the use of technology to prompt activity. Individuals within an office setting were encouraged to avoid prolonged periods of sitting through the use of a software program that reminded individuals to take a 1-minute break from sitting every 30 minutes. The point-of-choice prompts did result in lowering the number of prolonged uninterrupted sitting periods (10). In a study of academic and administrative staff at universities in four different countries (Australia, Canada, Northern Ireland, and the United States), a Web-based walking intervention focused on increasing walking by an extra 1,000 steps above baseline every 2 weeks during a 6-week period. For the employees who used the program, workday walking was increased by 25% (estimated to be equivalent to about 15 minutes more per day) (13).
To help understand the potential health impact of breaking up periods of prolonged sitting, researchers in the Take-a-Stand Project introduced the use of sit-stand devices (workstation design that allows employees to change from a standing to seated position) in a group of office workers whose jobs involved prolonged periods of sitting time (22). The sit-stand device did increase nonsitting time (by ∼66 minutes and 16.1% reduction in sedentary time during the intervention period) and also reduced upper back and neck pain and improved mood states (22). Although the study included a relatively small group of office workers (n = 10 for the control group and n = 24 for the intervention group) who were active (70% of control group and 75% of intervention group met the 2008 Physical Activity Guidelines for Americans level of activity), the study was conducted in a real-world setting and provides insights into potential benefits of reducing sitting time (22).
Although many questions remain related to the impact of sedentary behavior, exercise prescriptions should “…include a plan to decrease periods of inactivity in addition to an increase in physical activity” (3). Strategies for office workers have been suggested, including (9):
* Standing and taking a break from the computer every 30 minutes
* Taking standing breaks in sitting time during long meetings
* Standing during phone calls
* Walking to a colleagues’ desk instead of phoning or e-mailing
* Using a height-adjustable desk to enable frequent transitions between working in a standing or sitting position
* Using a headset or speaker phone during teleconferences to enable more standing during the meeting
Other action plan ideas for day-to-day life from ACSM are found in Box 5. From a public health perspective, policies and program implementation are recommended to educate the public of the health risks of inactivity (and how to reduce risks), to enhance opportunities for students to be active, to develop ways to allow sedentary employees to be active while maintaining productivity, and to develop community environments that are activity friendly (14).
A regular program of moderate to vigorous physical activity is recommended to help promote health and fitness. In addition, avoiding long periods of sedentary activity also seems to be important for health — for both physically active and inactive individuals (3). Recommendations on limits for sitting time or on the frequency of sitting-time interruptions are not yet defined precisely. Generally, individuals should be encouraged to limit sitting time and break up periods of prolonged sitting; a simple message has been suggested that promotes such activity: Stand Up, Sit Less, Move More, More Often (9).
ACSM has a full-color downloadable brochure, Reducing Sedentary Behaviors: Sitting Less and Moving More (see http://www.acsm.org/docs/brochures/reducing-sedentary-behaviors-sitting-less-and-moving-more.pdf).
Australian National Heart Foundation downloadable document “Sitting Less for Adults,” including tips to reduce sitting time when at home, at work, or while traveling (see http://www.heartfoundation.org.au/SiteCollectionDocuments/HW-PA-SittingLess-Adults.pdf).
American Heart Association Web site “Get Moving: Easy Tips to Get Active!” that includes tips for increasing physical activity at home, at work, and at play (see http://www.heart.org/HEARTORG/GettingHealthy/PhysicalActivity/StartWalking/Get-Moving-Easy-Tips-to-Get-Active_UCM_307978_Article.jsp).
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© 2014 American College of Sports Medicine.