摘要：Objectives. We estimated the amount of physical activity required for individuals to expend an additional 418.4 kJ (100 kcal) per day with the goal of achieving energy balance at the population level. Methods. Data on total daily energy expenditures were derived from a random sample of adults residing in Geneva, Switzerland, who completed a self-administered physical activity frequency questionnaire. These data were used to simulate the effects of typical physical activity pyramid recommendations on average population energy expenditures for various activity intensities and rates of population compliance with pyramid recommendations. Results. If an average 418.4 kJ (100 kcal) per day increase in energy expenditures is to be achieved, assuming 100% compliance with physical activity pyramid recommendations, the bottom tier of the pyramid must correspond to everyday activities performed at moderate to high intensity levels (e.g., moderate walking or biking). Expected population gains in energy expenditures would be only 167.4 to 251.0 kJ (40 to 60 kcal) per day at a 50% compliance rate. Conclusions. Achieving population-level energy balance through increasing energy expenditures with physical activity increases alone would require profound structural and environmental changes promoting more active lifestyles. Physical inactivity increases people’s risk of obesity, ill health, and premature mortality. 1 It is therefore paramount to determine the levels of physical activity that should be recommended to substantially reduce such risks at the population level. 2 – 4 Hill et al. 2 estimated that, on average, an extra 418.4 kJ (100 kcal) per day must be expended to restore energy balance and thus eliminate weight gain in Western populations. To achieve this goal, energy expenditures must be increased or energy intakes must be decreased. It remains unclear whether this goal can be achieved at the population level solely through increasing physical activity levels. For example, consider a hypothetical mass public health campaign intended to increase walking; expending an extra 100 kcal per day would require approximately 60 minutes of slow walking, or 30 minutes of moderate or brisk walking, with 50% compliance with the campaign’s recommendations at the population level. 3 To promote physical activity, national agencies have issued activity recommendations, 5 , 6 often translated into a pictorial model such as a “pyramid” 7 – 15 or a “rainbow.” 16 Figure 1 ▶ depicts a generalized model of a physical activity pyramid comprising 3 energy expenditure tiers. The bottom tier recommends engaging in everyday activities of at least moderate intensity (energy expenditures of 4184 kJ [1000 kcal] per week and above), such as climbing stairs, walking or bicycling to work, and gardening, for 210 minutes per week or more. The middle tier recommends engaging in endurance and cardiorespiratory recreational or competitive exercises and sports for at least 90 minutes per week in combination with strength training and flexibility exercises for at least 30 minutes per week. Open in a separate window FIGURE 1— Generalized physical activity pyramid model quantified for simulation purposes. Note . Only the bottom and middle tiers were considered in the simulations. Each of the 4 bottom-tier scenarios defining “moderate” physical activity in terms of minimum recommended basal metabolic rate (BMR) multiples of energy expenditures was examined in the simulations. Individuals already complying with the bottom-tier recommendations are urged to move to the middle tier and then the top tier to further increase their health benefits. For example, individuals already complying with the bottom- and middle-tier recommendations could, as recommended in the top tier, either engage in further higher-intensity exercise and sports or reduce the extent to which they engage in sedentary activities (e.g., watching television, talking on the telephone, playing or working at the computer). We simulated the potential population gains in total energy expenditure achievable by adults complying with the bottom- and middle-tier recommendations outlined in the pyramid depicted in Figure 1 ▶ . These simulations were based on extensive, real data on the total (i.e., not only leisure time) energy expenditures of a random sample of 8528 urban adults obtained with a survey instrument developed and validated in a separate random sample from the same population. 17 We estimated potential intervention effects after accounting for those adults already complying with the recommended level of physical activity.
