| | School Physical Activity Environment Related to Student Obesity and Activity: A National Study of Schools and StudentsReceived 13 November 2008; accepted 20 April 2009. published online 19 June 2009. Abstract PurposeTo explore whether characteristics of the U.S. secondary school physical activity environment are associated with student body mass index (BMI) and physical activity. MethodsThis report uses data from two studies: Monitoring the Future (MTF; an annual nationally representative survey of 8th-, 10th-, and 12th-grade public and private school students) and Youth, Education, and Society (a survey of administrators in schools that have completed their 2-year participation in the MTF study). School policies and programs related to various health issues, including physical education (PE) and sports activity, were examined for relationships with student self-reported height, weight, being active in sports, exercising vigorously, and participating in school athletics. ResultsThe results show that in 2004–2007, the percentage of students who attended schools that required PE in their grade differed sharply by grade level: 88% of 8th graders, 48% of 10th graders, and 20% of 12th graders. There were few statistically significant associations between school PE requirements and student BMI. The average percentage of students who participated in interscholastic or varsity sports was associated at the bivariate level with a lower percentage of students being overweight in all three grades. Other measures of PE and sports activity showed varying associations with BMI and physical activity measures. ConclusionsRelationships between the school physical activity environment and student BMI and physical activity were not uniformly strong. We conclude that, as currently practiced in schools, existing variations in physical activity policies may not be sufficient to produce discernible school-wide differences; thus, there is a need for more vigorous PE programming than is typically provided. Two factors are generally considered important contributors to the recent increases in obesity among American youth: insufficient physical activity and high caloric intake [1], [2], [3], [4]. Because young people spend a great deal of time in school, the school environment is a natural place to consider practices and policies that may affect students’ physical activity and food and beverage intake. In this paper, we examine secondary schools’ practices regarding physical education and sports participation, and we explore the extent to which those practices are associated with students’ self-reported overweight status and their exercise and sports habits [5].  Physical activity and the school environment Several objectives set in Healthy People 2010 focus on increasing physical activity (PA) among both children and adolescents [6]. The stated objectives include school-specific issues such as daily physical education (PE) and increased walking and bicycling to school. Additional recommendations from the U.S. Department of Health and Human Services [7] state that children should have a minimum of 60 minutes of PA daily, most of which should be moderate to vigorous physical activity (MVPA). Such objectives could be addressed within the school setting via PE and other activities such as intramural and varsity sports. Given that the Institute of Medicine recommends that children expend approximately 50% of daily energy at school [2], school-based PA provides an important opportunity to shape an individual's PA habits through completion of secondary school. Although school-based PE is required in virtually all states, participation requirements are generally low [8], [9], [10]. A nationally representative longitudinal study in Australia of both primary and secondary schools found that median total PA, fitness, and body mass index (BMI) were generally similar across schools regardless of the levels of compulsory PE and school sports provided, and concluded that current policies regarding school PA may not be of an intensity sufficient to relate to individual student PA or obesity [11]. Mixed results have been found regarding the relationship between walking or bicycling to school and student health. A national survey of U.S. youth in grades 4–12 found no relationship between walking or biking to school and BMI, but did find that such active transportation was related to a higher likelihood of frequent moderate physical activity [12]. Two small studies of primary school students (one of urban students in England, and one of suburban students in southern California) found that for boys, active commuting (walking in England; walking, biking, or skateboarding in California) was related to increased physical activity [13] and lower BMI [14]. A small study of rural Nebraska elementary school children showed surprising results, with active commuting associated with increased physical activity, but also associated with increased BMI among overweight children (no significant relationship was found with BMI among normal-weight children) [15]. Interventions targeting existing school PE curricula (e.g., adding additional PE classes, extending the length of PE classes, increasing time spent in PE classes in MVPA) have been found to relate positively to time spent in PA at school, as well as increased MVPA, energy expenditure, aerobic capacity and muscular endurance, flexibility, and PA knowledge and self-efficacy [8]. However, few relationships have been found between PE interventions and student BMI or body fat [8]. Some researchers posit that the lack of observed relationships between interventions that mandate dietary and PA changes in the school setting and student BMI may be due to students compensating by altering their behaviors outside of school [16]. Another possibility is that PE may be effective in increasing energy expenditures but may not be enough to affect weight. As noted above, the literature provides several examples of intervention studies to increase youth PA. However, no nationally representative study involving U.S. students has examined overall school PA environments and their relationships with student self-reported BMI and PA levels. This article is intended to provide that examination. In 2007, Johnston et al reported data on the levels of PE and sports participation among American secondary school students in 2003 through 2005 and the extent to which these levels varied by student grade level, racial/ethnic background, and socioeconomic status (SES) [17]. A principal finding was that PE was noticeably lacking in American high schools for all groups. In the present study, we again report data on the levels of secondary school student PE and sports participation (for 2004–2007) and extend the analysis to incorporate both (a) school-level variables as reported by school administrators and (b) student self-reports of BMI, exercise, and sports participation. The key research question to be addressed is: Are characteristics of the U.S. secondary school PA environment associated with relevant student outcomes, both bivariately and controlling for individual variables and other school-level variables? The conceptual model assumes that the school PA environment can have a direct effect on student outcomes, including BMI and PA levels. Thus, we hypothesize that schools with policies and practices that enhance student activity will have “better” outcomes, compared to schools that do not have such policies or practices. Other school-level factors may be confounded with PA variables, so we control for some key related measures. Of course, individual-level variables will also be associated with outcomes, so we also control for important factors at the individual level. Methods Samples and survey methods This report uses data from two studies, Monitoring the Future (MTF) and Youth, Education, and Society (YES). The MTF study annually surveys nationally representative samples of 8th-, 10th-, and 12th-grade students located in approximately 410 public and private schools in the 48 contiguous states; each school participates for 2 consecutive years. Thus, half of the sample of schools are “cycling out” of the study each year. In the YES study, administrators in schools that have just completed their second and final year of participation in the MTF study are requested to complete a questionnaire describing school policies and programs related to various health issues, including PE, food services, and substance use. MTF design and methods The design and methods for the MTF project are summarized briefly here; a detailed description is available elsewhere [18]. At each of three grade levels (8th, 10th, 12th), a stratified random sampling procedure is used that involves three stages: (1) geographic regions are selected; (2) schools are selected within regions with probability proportional to the estimated number of students in the target grade; and (3) students are selected within schools, usually by means of randomly selecting whole classrooms. A total of about 45,000 students are surveyed each year. Sample weights are assigned to each student to take into account variations in selection probabilities that occurred at all stages. Ethical approval for the study was obtained from the University of Michigan Behavioral Sciences Institutional Review Board [18], and informed consent was given for survey participation. Surveys were administered in group settings (that is, classrooms) by University of Michigan personnel; students self-completed the survey questionnaires during a normal class period. MTF student measures Gender, race/ethnicity, and parental education were reported. Students were coded as being of White, African American, Hispanic, or Other background; the numbers of cases in other specific race/ethnic groups were too small to allow separate estimates. Parental education, an average of father's and mother's educational attainment (with one missing data case permitted), is used as a proxy for SES, because students are generally unable to provide accurate information on family income and parental occupation. Students self-reported their height (in feet and inches) and weight (in pounds), using pre-coded close-ended response alternatives. BMI was calculated by dividing weight (in kilograms) by height (in meters) squared. Age- and gender-specific growth curves produced by the Centers for Disease Control and Prevention were used to determine whether each student's BMI was categorized as overweight (85th to less than the 95th percentile) or obese (equal to or greater than the 95th percentile) [19], [20]. Measures of student PA were obtained from responses to three questions: (1) How often do you actively participate in sports, athletics or exercising? (2) How often do you exercise vigorously (jogging, swimming, calisthenics, or any other active sports)? (3) To what extent did you participate in school athletic teams this school year? YES design and methods The half samples of nationally representative schools that were cycling out of the MTF study in 2004 through 2007 comprised the YES target sample. School administrators were asked to complete a self-administered questionnaire on a variety of school policies and relevant student participation rates. More than 85% of respondents were school administrators; teachers, and other school personnel were other respondents. The combined number of YES secondary schools that participated in the 2004–2007 surveys is 693, reflecting a response rate of 84%. A comparison of all schools responding to the YES questionnaire with all schools eligible for participation in the YES study showed minimal differences in student outcomes. For example, mean BMI was 21.6 in both groups for 8th grade, 22.9 for both in 10th grade, and 23.6 for both in 12th grade. Other student outcomes were similarly virtually identical. There were some very minor differences in school characteristics, but these were not sufficient to produce dissimilar student outcomes. YES measures Questionnaires were completed in late spring each year from 2004 through 2007, and administrators were instructed to answer for the current (just ending) school year. Respondents were asked whether students in the target grade (8th, 10th, or 12th) are required to take PE, what percentage of students actually take a PE class, the number of days per week they have PE, and the duration of a PE class (in minutes). These questions permit a calculation of the total number of minutes per week a student who takes PE would spend in PE. Questions were also asked about the rates of student participation, separately for boys and girls, in (a) interscholastic or varsity sports and (b) intramural sports or PA clubs. An additional question asked what percentage of students walk or bike from home to school on an average school day. Finally, a yes–no question was asked about whether the school gives physical fitness tests, and if so, whether parents are provided with the results. School-level control variables Type of school (public or private), size of school (number of students in target grade), percentage of students eligible for a free or reduced-cost lunch (an indicator of school SES), region of the country, and urbanicity were used as control variables in multivariate analyses. Region and urbanicity were derived from the sampling data from which the school was drawn. Four regions of the country were distinguished (Northeast, Midwest, South, and West) based on U.S. Census Bureau classifications. Three levels of population density were coded at the school level using locale code data from the National Center for Education Statistics: urban (large or midsize central city), suburban (urban fringe of either large or midsize city, as well as large or small town), and rural. Analyses All analyses were conducted using SAS version 9.1.3. Multivariate models took account of the complex sample design in estimation of parameters by using the survey logistic procedure, as well as using sampling weights [21]. The sample weights are designed to provide accurate inference at the student level. Each of the 11 relevant variables from the school administrator questionnaire was used as a predictor of each of the four student outcome variables, first bivariately and then multivariately, adding controls for other school- and student-level variables. All analyses were conducted separately by grade level, with data pooled across the four years (2004–2007). Results School and student data were available on the variables relevant to the present analyses from over 70,000 MTF student respondents in those schools. Female students comprised 50.6% of the combined samples. The racial/ethnic composition of the resulting student samples was 65.0% white, 10.6% African-American, 10.8% Hispanic, and 13.6% from other racial/ethnic backgrounds. Table 1 provides information on school administrators’ responses to questions on PA. The data are weighted to reflect the proportions of students who attend schools with various characteristics. | | |  | | Grade 8 | Standard error | Grade 10 | Standard error | Grade 12 | Standard error | |
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| School PE participation | | | | | | | | | % of Students required to take PE | 87.6 | 2.4 | 48.4 | 3.9 | 20.4 | 3.1 | | | Mean % of students who take PE | 91.8 | 1.5 | 64.1 | 2.9 | 34.0 | 2.8 | | | Mean number of days/week students have PE among those who take PE | 3.8 | .1 | 4.3 | .1 | 3.9 | .1 | | | Mean number of days/week that students have PE in all schools | 3.5 | .1 | 2.8 | .1 | 1.4 | .1 | | | Mean length of PE classes in minutes | 52.9 | 1.2 | 61.8 | 1.7 | 59.8 | 2.1 | | | Mean time students in all schools spend in PE classes (in minutes per week) | 179.9 | 5.3 | 173.0 | 9.2 | 82.0 | 7.2 | | | School varsity and intramural sports participation | | | | | | | | | Mean % of boys who participate in interscholastic or varsity sports | 36.2 | 1.6 | 38.8 | 1.7 | 35.9 | 1.6 | | | Mean % of girls who participate in interscholastic or varsity sports | 32.6 | 1.6 | 34.5 | 1.6 | 32.3 | 1.6 | | | Average % of both boys and girls who participate in interscholastic or varsity sports | 34.4 | 1.6 | 37.3 | 1.7 | 34.4 | 1.6 | | | Mean % of boys who participate in intramural sports or physical activity clubs | 27.4 | 1.8 | 16.5 | 1.5 | 15.8 | 1.9 | | | Mean % of girls who participate in intramural sports or physical activity clubs | 22.9 | 1.6 | 13.8 | 1.4 | 13.8 | 1.8 | | | Average % of both boys and girls who participate in intramural sports or physical activity clubs | 25.2 | 1.7 | 15.6 | 1.5 | 15.0 | 1.8 | | | Walking or biking to school | | | | | | | | | Mean % of students who walk or bike from home to school on an average school day | 19.3 | 1.6 | 12.2 | 1.4 | 8.6 | 1.3 | | | School physical fitness tests | | | | | | | | | % of Students who attend schools that provide physical fitness tests to at least some students | 64.8 | 3.5 | 41.6 | 3.9 | 23.4 | 3.2 | | | % of Students in schools in which at least some parents are provided with the results of physical fitness tests | 39.2 | 3.5 | 20.6 | 3.3 | 10.2 | 2.3 | | | | |
For the years 2004 through 2007 combined, 88% of 8th-graders attended schools that required PE in their grade, compared to 48% for 10th graders, and 20% for 12th graders. The mean percentage of students reported to take PE showed similar sharp differences by grade at 92%, 64%, and 34%. Other results from the school administrator surveys can be seen in Table 1. Table 2 provides descriptive data from student self-report information on the outcomes of interest: BMI and overweight status, and measures of PA for the total sample by grade. Slightly more than 10% of students in each grade were obese, and approximately 25% were overweight (or obese). Analyses by gender within grade (not shown) indicated that males averaged slightly higher in BMI than females but were distinctly more likely to exceed the 85th and 95th percentile cutoffs. Male students also were generally more likely than female students to report actively participating in sports, exercising vigorously, or having much participation in school athletic teams. Table 3, Table 4, Table 5, Table 6 provide results of logistic regression analyses addressing the key research question. We first report the association between each environmental variable and the percentage of students who were at or above the 85th percentile, and then between each of the environmental variables and the three measures of being active in sports, exercising vigorously, and participating in school athletics. In general, the school PE variables did not show statistically significant associations with students’ overweight status, particularly after controls for other school- and student-level variables were included in the regressions. Similarly, the percentage of students walking or biking to school, along with school fitness test measures, were usually not statistically significant. The average percentage of students (both boys and girls) who participated in interscholastic or varsity sports was associated at the bivariate level, with a lower percentage of students being overweight or obese in all three grades. This association remained significant after controls for individual-level variables for 10th and 12th graders. The average percentage of students (both boys and girls) who participated in intramural sports or PA clubs was associated bivariately with a lower percentage of students being overweight or obese in all three grades, but significantly so in 8th grade only. This association remained significant after controls for individual-level variables, but not after school-level variables were added. The PE measures were, for the most part, not significantly systematically related to the students’ self-reported exercise variables (Table 4, Table 5, Table 6). One exception was that the mean length of PE classes was negatively associated with being active in sports and participating in school athletics in all three grades; that is, longer PE classes were associated with students reporting being less active and participating less in school athletics. Only one of the nine associations with exercising vigorously was significant (at p < .05), suggesting no important relationships. The average percentage of students (both boys and girls) estimated by school administrators to have participated in interscholastic or varsity sports was generally associated at the bivariate level with significantly higher percentages of students self-reporting being active in sports, exercising vigorously, and participating in school athletics; and most of the associations remained significant after controlling for individual- and school-level variables. The average percentage of students (both boys and girls) who participated in intramural sports or PA clubs was generally not associated with the percentages of students being active in sports, exercising vigorously, or participating in school athletics. (Bivariate associations were significant among 8th graders—who have higher rates of participation—for being active in sports and exercising vigorously, but these did not remain significant in multivariate models.) Discussion The results show that from 2004 through 2007, the percentage of students who attended schools that required PE in their grade differed sharply by grade level: 88% of 8th graders, 48% of 10th graders, and 20% of 12th graders. This finding is fully consistent with previous reports [17]. Clearly, in recent years, required PE has become a rarity for American high school seniors. However, it is difficult to say whether this has major implications for obesity rates among students, given the lack of significant association between the requirement and the percentage of students who are at or above the 85th percentile on BMI after controlling for both individual- and school-level variables. In bivariate models, the percentage of overweight students was higher in schools that did not require PE than in schools that did: 29.7% versus 26.5% in 8th grade, 28.1% versus 25.5% in 10th grade, and 24.9% versus 23.0% in 12th grade. These are modest differences, and become nonsignificant for 8th and 12th grade when individual variables are controlled. The differences become nonsignificant in all grades when school-level variables are added to the individual-level controls. The percentage of students who actually take PE showed a similar pattern. Another indicator of extent of PE (number of days per week that students take PE, averaged across all students) also showed a negative association with percent at or above the 85th percentile, significantly so for 10th graders. Other indicators (length of PE classes, amount of time spent in PE) generally showed no association with the percentage of students at or above the 85th percentile. It should be noted that analyses examining the associations of the various school PE-related measures and both continuous BMI score and classification as obese produced similar results. Thus, it appears that, as measured in the present study, variations in PE in American secondary schools have at best only modest association with student BMI. These findings are consistent with those noted in the Introduction obtained from nationally representative work in Australia [11]. Why do we see so little association? A number of factors should be considered. One might argue that controlling for school-level variables such as percentage of students eligible for a free or reduced-cost lunch is in some sense “overcontrolling” because any effect of a PE requirement might overlap or be shared with school SES. However it does seem entirely reasonable to control for individual-level variables, and such controls make the PE requirement effect nonsignificant for 8th and 12th graders. It may be useful to note that school-level variables in general cannot explain much variance in student outcomes when much of the variance in the outcomes is within schools. This is certainly the situation with the percent of overweight students: O'Malley et al [22] reported that less than 4% of the variation in BMI or in the percentage of students at or above the 85th percentile lies between American secondary schools, while more than 96% is within schools. Similarly, in the present study only 3–4% of the variance in being active in sports and in exercising frequently is between schools at each grade. Participation in school athletic teams varied somewhat more, at 5–9% between schools. This study has other limitations that could reduce our ability to detect associations. The data are cross-sectional, making it difficult to discern even the directionality of any associations. An additional important limitation is reliance on one or two observers to provide information that may be difficult for them to know with high accuracy. We have tried to limit our requests for information to data that should be fairly readily known. However, information such as what percentage of students walk or bike to school, or what percent participate in intramural sports will clearly have some degree of reporting error. However, the percentage of students that administrators reported as participating in interscholastic or varsity sports was positively associated with the percentage of students who self-reported being active in sports, exercising vigorously, and participating in school athletic teams. This suggests that the administrator reports are indeed reasonably valid indicators of student participation. We were also limited in the extent of information that was obtained. For example, details about extent of teacher training or accreditation for PE, length of time students participated in PE (full year, half year), and other factors were not obtained. Although we attempted to assess the most important potential factors, the range of policies addressed in this study is relatively narrow. Still another limitation is that we are to some extent analyzing reports of policies that may not be fully realized in practice. Furthermore, although this study is large by most standards, the number of schools per grade combined across all 4 years is less than 250; thus, small effects may not rise to the level of statistical significance. Another possible contributing factor to our lack of findings is that PE as practiced in schools is simply not physically demanding enough to have a discernible effect on BMI. Several studies indicate that in order to find significant relationships between PE and body fat, PE programs need both significant daily class commitment (e.g., 1.25 hours per day [23]) and purposeful increases in MVPA [24], [25]. Studies that increased the percentage of MVPA per PE class, but did not increase the total number of PE classes required, showed no significant differences in body size [26], [27]. In fact, the Institute of Medicine Committee on Prevention of Obesity in Children and Youth recommends that half of children's daily PA should be accrued during the school day [2]. Many school districts may be concerned that requiring daily PE would result in decreased academic performance due to time limitations; however, research indicates that significant allocation of curricular time to PA may actually enhance learning rates [28], [29]. There are also limitations with respect to the students’ self-report measures. Regarding height and weight, a number of studies have investigated use of self-reports, and have generally reported that, although there may be biases in absolute levels associated with self-reports, the data are certainly adequate for research purposes. Brener et al [30] obtained both objective and self-reported data on height and weight for more than 2000 students in grades 9 through 12, and found that “…self-reported values of height, weight, and BMI were highly correlated with their measured values” (p. 281). Brener et al [30] also noted that surveillance systems can yield “…valuable results by using self-reported height and weight to assess trends in the prevalence of obesity” (p. 287). Goodman et al [31] analyzed data from more than 10,000 respondents in the National Longitudinal Study of Adolescent Health, with both self-reported and objectively measured height and weight. They report that “correlations between measured and self-reported anthropomorphic indices [height and weight] were very strong” (p. 54). They conclude that “findings from other studies that have used self-reported BMI should be considered valid, and future studies can use self-reported data to understand adolescent obesity, its correlates, antecedents, and sequelae” [31 (p. 57)]. Although the findings are supportive of use of self-reports for research, there is also evidence of bias. Ogden et al [32] reported that about 34% of 12–19-year-olds were overweight or at risk of overweight based on actual measurements, compared to the 25% found here, based on self-reports. The students self-reported their levels of physical activity, exercise, and sports participation in broad, general terms. It would of course be preferable to have more specific information, but we believe that the measures likely capture much of the valid interindividual variation. (Using procedures developed by Heise [33] and Wiley and Wiley [34], we estimate the reliabilities of the single-item measures of exercise and sports at .60 for each, based on longitudinal data gathered at 2-year intervals; we do not have an estimate of the reliability of the participation in school athletic teams item, because we do not have longitudinal data for that question). It is possible that increased sensitivity in the self-reported PA measures might improve the ability to detect relationships with school-level PA environment measures. Although the physical education measures showed limited associations, the average percentage of students who participated in interscholastic or varsity sports showed the expected relationship, with a lower percentage of students at or above the 85th percentile in all three grades, and remained significant after controls for individual-level variables for 10th and 12th graders. The average percentage of students (both boys and girls) who participated in intramural sports or PA clubs was associated with a lower percentage of students being overweight; this was significant only in 8th grade, bivariately and with individual-level variables controlled. None of these associations remained significant after controlling for both individual- and school-level variables, but as noted above, controlling for the school variables may be in some sense “over-controlling.” The overall pattern suggests that, in schools with high percentages of students participating in sports (based on administrators’ reports), there are likely to be somewhat lower levels of student overweight, though the associations were not always statistically significant. The percentage of students walking or biking to school was not associated with the percentage at or above the 85th percentile for any grade. Low rates of walking or bicycling to school reflect previously published rates [35], and likely limit the possible overall effects of these activities. There may be salutary effects of an individual student walking or biking to school, especially if the distance is substantial, but the effects (particularly because the effects are likely to be small) may be obscured by our use of a school-level measure of percentage of all students walking or biking. If rates of walking and bicycling reached the Healthy People 2010 goal of 50% (rates were at 48% in the late 1960s [36]), direct relationships might be possible to detect. Research among youth in the Philippines has shown that commuting to school via motorized transportation versus walking may result in an expected weight gain of 2 to 3 lb yearly [37]. Whether a school provided physical fitness tests and whether a school provided parents with results of such tests did not appear to have any meaningful association with percentage of students being at or above the 85th percentile. Requirement of PE, the percentage of students who take PE, mean PE class length, and total time spent in PE classes were for the most part not systematically associated with the percentage of students reporting being active in sports, exercising vigorously, or participating in school athletics, particularly after controls for individual- and school-level variables. The number of days per week that students take PE did show significant associations, before and after controls, with the percentage of students reporting being active in sports and exercising vigorously, but only among 8th graders. One possibility is that although the mean number of days per week that students have PE is generally similar across grades among students who take PE, 8th-grade students are much more likely both to be required to take PE and to actually take PE. Thus, the lack of findings for 10th and 12th graders between days per week PE is taken and participation in sports or vigorous exercise may be related to the lower number of students exposed to higher numbers of days of PE. This finding may indicate that if the Healthy People 2010 recommendation of daily PE participation were to be broadly implemented, students might have higher levels of overall PA, as well as MVPA. Another possibility relates to the findings from prior research on PA compensation. In an intervention study with 3rd- to 5th-grade youth in two school districts in Nebraska, Donnelly et al [38] found that intervention schools were able to improve lunch nutrition (lowered food energy, fat, and sodium; increased fiber) significantly, and to improve class-based PA slightly. However, measures of 24-hour energy intake showed no differences for food energy, fat, or fiber; further, PA outside of school was significantly lower for intervention students than control. The authors concluded that students may downwardly adjust their spontaneous PA outside of the school environment in response to increases in school-related structured PA. However, a California-based intervention to increase PA both in PE classes as well as outside of school with elementary school children in seven small schools indicated no differences between intervention and control subjects on PA outside of school over a 2-year period [39]. Thus, the limited evidence for a phenomenon of compensation is mixed. Findings from the present analyses may reflect such compensation, especially for high school students with increased academic demands. Participation in intramural sports or PA clubs was generally not related to student self-reports of being active in sports, exercising vigorously, or participating in school athletics for the high school students. There was some association at 8th grade, where the participation is greatest. It seems likely that intramural sports have a substantially lower level of PA compared to varsity sports, which would attenuate the relationships. The percentage of students walking or biking to school, and whether a school conducted or reported results of physical fitness tests did not appear to be systematically associated with any of the three student self-report measures. This is not surprising; these self-report measures may not measure with great accuracy actual levels of walking or biking to school. Conclusion In summary, rates of PE participation remain low, and decline sharply with grade level. We have not been able to demonstrate clear effects of a number of aspects of school environment on student overweight, particularly those having to do with PE and walking or biking to school (now a rare behavior). There are, however, demonstrable associations with student participation in varsity and intramural sports. These associations suggest that this might be a fruitful area for intervention studies. We remain convinced that PA is an important part of the effort to reduce child obesity, and that schools can play an important role in that effort. We have shown that, as currently practiced in schools, existing variations in PA policies may not be sufficient to produce discernible school-wide differences. We suspect that schools need to have policies that support more vigorous PA than do current policies. A number of studies support the value of enhanced quantity and quality of physical education to increase physical activity. In addition, researchers such as Leupker et al [26] have noted that improving lifetime PA habits among youth may have an important and significant cumulative impact over and above any reduction in immediate physiological risk levels. Healthy People 2010 calls for increasing the proportion of adolescents who spend at least 50 percent of school physical education class time being physically active [40]. Schools should be encouraged to provide their students opportunities for more moderate to vigorous PA in PE, and the motivation to incorporate PA into their lives, both in and out of schools. Acknowledgments This research was conducted as part of the Youth, Education, and Society (YES) project (part of a larger research initiative called Bridging the Gap: Research Informing Policy and Practice for Healthy Youth Behavior) funded by the Robert Wood Johnson Foundation. The Monitoring the Future study is funded by the National Institute on Drug Abuse (DA01411). The views expressed in this article are those of the authors and do not necessarily reflect the views of the sponsors. We thank Kathryn Johnson for editorial assistance. References [1]. [1]Johnston LD, O'Malley PM. Obesity among American Adolescents: Tracking the Problem and Searching for Causes. Youth, Education, & Society Occasional Paper No. 3. Ann Arbor, MI: Institute for Social Research, 2003. Available at: http://www.yesresearch.org/pubs.html#reports. Accessed October 30, 2008. [2]. [2]In: Koplan JP, Liverman CT, Kraak VI editor. Preventing Childhood Obesity: Health in the Balance. Washington, DC: National Academies Press; 2005;. [3]. [3]Patrick K, Norman GJ, Calfas KJ, et al. Diet, physical activity, and sedentary behaviors as risk factors for overweight in adolescence. Arch Pediatr Adolesc Med. 2004;158:385–390. MEDLINE |
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