Move More, Sit Less: A First-Line, Public Health Preventive Strategy?

Despite the widely cited Centers for Disease Control and Prevention (CDC)/American College of Sports Medicine (ACSM) exercise guidelines,1 the much-heralded surgeon general's report,2 and the recently published ACSM/American Heart Association exercise statement3 and federal physical activity guidelines (Table I),4 the conventional model for getting people to be more physically active (ie, structured exercise program) has been only marginally effective. Traditional exercise programs have typically reported dropout rates of 50% or more at 1 year, highlighting the compliance problem among those who voluntarily initiate exercise, regardless of health status. Other enrollees, who do not technically meet the criteria for "exercise dropout," may continue exercising at a subthreshold intensity, frequency, or duration. According to the CDC, only 31% of American adults meet contemporary physical activity recommendations (ie, moderate-intensity activity for ≥30 min/d, 5 or more d/wk, or vigorous activity for ≥20 min/d, 3 or more d/wk), and 24% of the adult population reportedly engage in no leisure time physical activity.5 Men are more likely to meet the recommendation than women, and black and Hispanic or Latino persons demonstrate the lowest prevalence of regular leisure time physical activity: 25% and 23%, respectively. Morbidly obese individuals in particular are often completely sedentary. According to a recent report,6 morbidly obese adults (mean±SD body mass index, 53.6 ± 11.7 kg/m2) were asked to wear an activity sensor that monitored their caloric expenditure, minute-by-minute physical activity, and number of steps per day. The participants spent an average of 23 hours and 52 min/d sleeping, sitting, lying down, or performing sedentary activities (<3 metabolic equivalents [METs; 1 MET=3.5 mL O2/kg/min]). Collectively, these data suggest that structured exercise is not unlike other health-related behaviors in that only a fraction of those who initiate the behavior will continue, regardless of their age, sex, race, ethnicity, education level, or health status. To understand why people sometimes lack the motivation for a structured exercise commitment, one must first acknowledge a simple yet important fact: exercise is voluntary and time-consuming. Therefore, planned exercise may extend the day or compete with other valued interests and responsibilities of daily life. In addition, considerable time may be spent in transit, driving to and from a health club or recreation facility. In one study, coronary patients undergoing medically supervised gymnasium-based exercise training spent more time in their cars going to and from the programs than patients in a home training comparison group spent on their cycle ergometers.7 Other investigators have reported that structured rehabilitation exercise training is associated with a low caloric expenditure and has little impact on body weight and selected coronary risk factors.8,9 Numerous epidemiologic and clinical studies suggest that the interrelationship among training intensity, frequency, and duration may permit a decrease in intensity to be partially or totally compensated for by increases in the duration or frequency of exercise or both. Thus, it appears that the benefits of physical activity may depend more on the total amount of exercise accomplished or calories expended than on the specific exercise intensity, frequency, or duration. Moreover, individuals in the least fit, least active cohort (bottom 20%) are expected to derive the greatest health benefits from a given increase in physical activity.1,10 The skyrocketing prevalence of overweight/obesity, diabetes mellitus, and other chronic diseases suggest the need for more accessible interventions to circumvent and attenuate conventional barriers to achieving an adequate daily energy expenditure. Although vigorous leisure time physical activity (eg, noon-hour jog) has been widely promoted to achieve a physiologic training effect, a reasonable alternative, especially among habitually sedentary individuals, is to integrate multiple short bouts of light- to moderate-intensity physical activity into their daily lives (Figure 1).11 If the associated energy expenditure (lifestyle physical activity vs structured leisure time exercise) is comparable, similar health benefits should accrue. Moreover, if an adequate part of the energy expenditure is performed above a minimum threshold intensity (∼30%–45% of oxygen uptake reserve),12 a concomitant increase in cardiorespiratory fitness would be expected. Theoretical patterns of physical activity for sedentary people (solid line), people who engage in regular leisure time exercise (eg, noon-time jog; dotted line) but are otherwise sedentary, and people who integrate several shorter bouts of lower-intensity physical activity into their daily routines (dashed line). Lifestyle activities may include brisk walking, stair-climbing, gardening, household chores, washing the car, and table tennis. These may be as effective as structured leisure time exercise in promoting health benefits provided that the total energy expenditure is comparable. Adapted from reference.11 Randomized clinical trials have now shown that a lifestyle approach to physical activity among previously sedentary individuals has similar effects on cardiorespiratory fitness, body composition, and coronary risk factors as a traditional structured exercise program.13,14 These findings have important implications for public health, suggesting another approach for sedentary persons who are not ready to comply with a formal exercise program.15 Thus, physicians and allied health professionals should consider broadening their recommendations, from the traditional frequency, intensity, duration, and modes of exercise training that are associated with a more formal exercise commitment to promoting increased activity in daily living.16 Pedometers can be helpful in this regard, as can programs that use them (eg, America on the Move) to enhance awareness of physical activity by progressively increasing daily step totals. In a systematic review of randomized controlled trials, pedometer users significantly increased their physical activity by nearly 2500 steps per day more than control participants.17 Physically demanding work has been reduced or eliminated in many sectors and replaced by labor-saving devices focused on speed, rapid communication, improved efficiency, and increased productivity.16 Opportunities for increased physical activity can be achieved via 4 major domains throughout the day: at school or work (whether or not the work involves manual labor); for transport (walking or cycling to work or to shop); during domestic responsibilities (housework, landscaping chores); and during leisure time pursuits (golf, tennis, walking). For example, the Geneva stair study reported that previously sedentary adults who exclusively used stairs instead of elevators at work demonstrated increases in aerobic capacity and decreases in body weight, waist size, and resting blood pressure.18 Worksite interventions that include contemporary workstations that require standing or extremely slow walking (<1 mph) at the computer may serve to literally double energy expenditure over the 8-hour workday!19 The activity pyramid has been suggested as a model to facilitate public and patient education for the adoption of a progressively more active lifestyle.20Figure 2 reflects the stepwise weekly set of goals for the promotion of improved cardiorespiratory fitness and health to reduce the risk of cardiovascular disease and other chronic diseases that are associated with a sedentary lifestyle. The base of the pyramid emphasizes the important public health goal of accumulating at least 30 minutes on most (≥5), and preferably all, days of the week. This includes brisk walking, taking the stairs more often, and performing home-care activities. The second tier includes structured aerobic activities and/or recreational sports performed 3 to 5 days per week. Complementary leisure time activities, such as golf or bowling, and calisthenics and resistance training are recommended in the third tier at a lesser frequency. Collectively, these activities should reduce the amount of leisure time spent at the top of the pyramid, that is, sitting (eg, watching television or using the Internet). The activity pyramid, analogous to the US Department of Agriculture's Food Guide Pyramid, has been suggested as a model to facilitate public and patient education for adoption of a progressively more active lifestyle. ©1996 Park Nicollet Health-source ®Institute for Research and Education (reprinted with permission). Recent studies have shown that sedentary behaviors alone, especially sitting,21–31 independent of aerobic capacity or leisure time physical activity (Figure 3),32 are associated with higher rates of all-cause and cardiovascular mortality, obesity, type 2 diabetes, endothelial dysfunction, and metabolic syndrome as well as other physiologic derangements that are due to our increasingly hypokinetic lifestyle.33 About half the leisure time of the average American is spent watching television, more often than not using a remote control device. Other popular sedentary pastimes include viewing sports, reading, listening to MP3 players, using cell phones, engaging DVD players, playing video games, e-mailing/text messaging others, using the Internet, and gambling.16 Understanding the unique molecular, physiologic, and clinical effects of too much sitting (inactivity physiology) may help to clarify the risk for and impact of associated chronic diseases, particularly in an era of technologic advancements that has resulted in the widespread elimination of occupational and leisure time physical exertion. The risks of cardiovascular disease decrease linearly in association with increasing percentiles of physical activity. There is a precipitous drop in risk when comparing the lowest with the next-lowest category (0 → 25th percentile) for aerobic capacity. Beyond this demarcation, the reductions in risk parallel those observed with increasing physical activity but are essentially twice as great for aerobic capacity. A major question raised by the inactivity physiology paradigm is whether excessive sitting will worsen the risk at any given percentile, causing the curves to shift upward and to the right. Adapted from reference 32. Non–exercise activity thermogenesis (NEAT), the spontaneous physical activities of daily living (eg, fidgeting while sitting, standing while reading, moving the lower extremities while working at the computer), represent another source of energy expenditure for many people.34 A pioneering series of laboratory studies showed that experimentally reducing NEAT had a negative impact on lipid metabolism by suppression of skeletal muscle lipoprotein lipase, independent of vigorous exercise training.23,35 These findings suggest that the low-intensity standing and ambulating done intermittently throughout the day may be as important for disease prevention and optimization of health as is structured exercise. Simply standing in an erect posture requires the activation of several large groups of skeletal muscle to contract cumulatively, all of which alter metabolism and augment energy expenditure. Presumably, >90% of energy expended in all forms of physical activity occurs during standing and nonexercise ambulation, highlighting how little energy sedentary individuals expend during NEAT while sitting.36 Healy and colleagues25 provided accelerometers to adults with diabetes to examine the association of metabolic risk with measured physical activity and sedentary time. Following baseline measurements, participants' activity levels were monitored for 7 consecutive days to determine the percentage of time spent sedentary and in light-intensity and moderate- to vigorous-intensity activities, in addition to the mean activity intensity. Waist circumference, resting blood pressure, high-density lipoprotein cholesterol, triglycerides, fasting plasma glucose, and a clustered metabolic risk score were then associated with collected accelerometer data. Results demonstrated a significant association among mean activity intensity, sedentary time, and light-intensity time with both waist circumference and clustered metabolic risk. This relationship was independent of time spent engaged in moderate- to vigorous-intensity activity, indicating that regardless of participation in structured exercise, those with higher percentages of sedentary or light-intensity activity time throughout the day had more deleterious health outcomes. Another investigation by Healy and associates26 monitored interruptions in sedentary time to determine the association of "taking a break" with several markers of metabolic risk. Accelerometers were worn by participants during a 7-day period, recording time spent sedentary in addition to frequency of breaks >1 minute in sedentary time. Participants who took more frequent breaks exhibited significantly smaller waist circumference and body mass index measurements, as well as lower triglyceride and 2-hour plasma glucose levels. These results were independent of total sedentary time and moderate- to vigorous-intensity time, providing evidence that simply increasing the frequency of breaks from sedentary behaviors may markedly improve indices of metabolic health. Collectively, these data24 suggest that it is time we consider sitting and too few breaks from sitting a serious health hazard. While public health guidelines encourage participation in a minimum of 30 minutes of daily moderate-intensity physical activity, there are no existing activity recommendations for the remaining 16.5 hours that the average individual spends awake. Many persons may spend more than 90% of their waking hours sitting (Table II). Energy expenditure during nonexercise time may be as critical for preventative health as the structured exercise time.37 Accordingly, physicians should encourage patients to reduce sitting and increase breaks from sitting both at home and in the workplace. Although lifestyle exercise is not necessarily being suggested as a replacement for structured exercise programs, alternative strategies are needed to encourage escalating numbers of habitually sedentary adults to increase their level of physical activity. Lifestyle physical activity, such as moderate to vigorous exercise regimens, can produce measurable improvements in indices of health and fitness.11,13–15 In addition to the promotion of moderate to vigorous structured exercise and increased lifestyle physical activity, physicians and allied health professionals should discourage sitting for extended periods (or too few breaks from sitting). Breaks may include walking, filing, photocopying, stair climbing, standing, or combinations thereof. To assist with this objective, a 7-step counseling plan has been suggested to help patients initiate and maintain a more physically active lifestyle: Ask patients about their current structured exercise and activity habits to determine whether these are sufficient to meet contemporary exercise guidelines. Offer counseling and educational gatherings that include both patients and spouses to create and maintain positive attitudes that support exercise adherence.38 Provide patients with a traditional exercise prescription, initially advocating a moderate-intensity activity regimen. Counsel patients to identify opportunities to increase occupational and leisure time physical activity, including the use of a pedometer17 and/or active commuting to work (walking or cycling),39,40 as well as ways to overcome current obstacles or limitations to physical activity. Advise patients not only to embrace a structured exercise program and increased lifestyle physical activity but to reduce the amount of time spent in sedentary behaviors and sitting in particular. Emphasize the short- and long-term benefits of increasing levels of physical activity and fitness, especially the value of moving out of the least fit, least active, "high-risk" cohort (bottom 20%).1,10 Plan follow-up contact to reinforce positive efforts and devise strategies to combat recidivism. The challenge for the medical community is to engage an escalating number of patients in home-, work-, and community-based interventions so that many more individuals may realize the cardioprotective and general health benefits that increased physical activity can provide. Legislators, public health and planning professionals, and community representatives can help to facilitate this objective by creating more walkable and bikeable communities. Employers can make the workplace less sedentary by embracing the American Heart Association's newest cause initiative, Start! (http://www.americanheart.org/start), which promotes a culture of physical activity, healthy nutrition options, and corporate wellness.19,41 Patients should be counseled that an active way of life brings health benefits, even for those who remain overweight/obese. Numerous studies have now shown that less fit individuals are approximately 2 to 5 times more likely to die during follow-up compared with their more fit counterparts, matched for age, sex, and body habitus (normal weight, overweight, or obese).42–45 Contemporary findings highlight the importance of avoiding prolonged uninterrupted periods of sedentary (primarily sitting) time, as well as increasing time spent in structured exercise and lifestyle physical activity, in combating chronic diseases. It is time for a new paradigm in exercise prescription beyond target heart rates and metabolic equivalents: move more, sit less.