NHANES, Behavior Risk Factor Surveillance System (BRFSS), and the Family Interaction, Social Capital and Trends in Time Use Data (1998-1999), together with trend data on sports and recreational participation, suggest a significant increase in reported leisure-time physical activity in adults (Pratt et al., 1999; French et al., 2001a; Sturm, 2004).

Cross-sectional data from the National Human Activity Pattern Survey, based on the responses of 7,515 adults between 1992 and 1994, assessed time use and daily energy expenditure patterns of adults. Results suggested that sedentary and low-intensity activities dominated while leisure-time, high-intensity activities accounted for less than 3 percent of energy expenditure (Dong et al., 2004).

Americans are presented with trade-offs in how they allocate their time and money. Understanding how Americans in general, and children and youth in particular, use their leisure time will help to determine ways of promoting more physical activity into their lives. An analysis of time allocation and expenditure patterns for U.S. adults over the past several decades suggests that they are spending more time in leisure and travel or transportation and less time in productive home activities (e.g., meal preparation and cleanup) and occupational activities (Sturm, 2004). Leisure-time industries have exceeded gross domestic product growth for both active industries (e.g., bicycles, sporting goods, membership sports clubs) and sedentary industries (television, spectator sports). However, there has been a steeper growth in sedentary industries from 1987 to 2001—especially the growth of cable television and spectator sports (Sturm, 2004).

Trend data for children (spanning from 1981 to 1997) have shown that they now have less discretionary or free time—defined as time not spent eating, sleeping, attending to personal care, or at school—than they used to because more of their time is spent away from home in school, after-school programs, or daycare. There is also a noted increase in the amount of time children spend in organized sports (Hofferth and Sandberg, 2001; Sturm, 2005a), but active transportation (e.g., bicycling or walking) is not a significant source of physical activity for children and youth (Sturm, 2005b).

Modern technologies such as labor-saving home appliances have reduced the energy expended for home meal preparation and the amount of time needed to achieve the same task (Sturm, 2004). Other technological innovations such as home entertainment devices (including cable television, computers, video games) and automobiles have contributed to sedentary behaviors among Americans, causing them to expend less energy. This phenomenon of increased time spent in passive sedentary pursuits relative to active leisure activities has been associated with the rise in obesity (French et al., 2001a; Philipson and Posner, 2003). However, although the average American adult spends more than 20 hours per week watching television, videos, or digital video discs (DVDs), it is notable that the largest increase

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