BRFSS data, although it is unclear why this occurred (CDC, 2004b). In 2001, BRFSS respondents were asked to report the overall frequency and duration of time spent in household, transportation, and leisure-time activity of both moderate and vigorous intensity (CDC, 2003c). Although 45.4 percent of adults reported having engaged in physical activities consistent with the recommendation of a minimum of 30 minutes of moderate intensity activity on most days of the week in 2001, more than one-half of U.S. adults (54.6 percent) were not sufficiently active to meet these recommendations (CDC, 2003c).
The physical activity trend data for children and youth are even more limited than for adults. Most available information is on the physical activity levels of high school youth, with limited data available on levels in younger children. Based on the Youth Risk Behavior Survey (YRBS), daily enrollment in physical education classes declined among high school students from 42 percent in 1991 to 25 percent in 1995 (DHHS, 1996) and increased slightly to 28.4 percent in 2003 (CDC, 2004c). Cross-sectional data collected through the YRBS for 15,214 high school students indicated that one-third (33.4 percent) of 9th to 12th graders nationwide are not engaging in recommended levels of moderate or vigorous physical activity