One- and two-year predictors of decline in physical activity among inner-city schoolchildren

One- and Two-Year Predictors of Decline in Physical Activity Among Inner-City Schoolchildren Tracie A. Barnett, MSc, Jennifer O’Loughlin, PhD, Gilles Paradis, MD, MSc Background: Alarming secular declines in physical activity (PA) have been observed among youth over the last decade. A better understanding of the predictors of these declines is crucial to identifying those children most at risk and to developing interventions that target youth before the onset of decline. This report identifies 1- and 2-year predictors of decline in PA among fourth- and fifth-grade students from inner-city neighborhoods in Montreal, Canada. Methods:

Data for this study were collected in classroom questionnaires each May/June from 1993 to 1997. Analyses for this paper were completed in 2001. The cohort included active (at least one PA per day) children with baseline and 1-year (n ⫽1873) or 2-year (n ⫽509) follow-up data.

Results:

In boys, 1-year predictors of decline to an inactive status identified in generalized estimating equations analysis included moderate (vs high) baseline PA (odds ratio [OR]⫽1.66, 95% confidence interval [CI]⫽0.91–3.05); low PA self-efficacy (OR⫽1.67, 95% CI⫽1.03–2.71); born outside Canada (OR⫽2.13; 95% CI⫽1.31–3.46); Asian origin (OR⫽1.81; 95% CI⫽1.03–3.16) and no participation in school teams (OR⫽1.81, 95% CI⫽0.93–3.55). In girls, these 1-year predictors included moderate PA (OR⫽1.91, 95% CI⫽1.10 –3.32); low PA self-efficacy (OR⫽1.70, 95% CI⫽1.15–2.49); watching four or more TV programs per day (OR⫽1.40, 95% CI⫽0.97–2.02); mother unemployed (OR⫽1.54, 95% CI⫽1.07–2.23); and grade five (vs grade four) (OR⫽1.35, 95% CI⫽0.94 –1.93). Two-year predictors in boys included moderate baseline PA (OR⫽2.52, 95% CI⫽0.84 – 7.50), and born outside Canada (OR⫽1.96, 95% CI⫽0.91– 4.20). In girls, these 2-year predictors included moderate baseline PA (OR⫽2.75, 95% CI⫽1.01–7.49); no participation in school teams (OR⫽2.14, 95% CI⫽0.92–5.00); watching four or more TV programs per day (OR⫽1.93, 95% CI⫽0.99 –3.74); and born outside Canada (OR⫽1.85, 95% CI⫽0.96 –3.55).

Conclusions: Reduced TV viewing among girls and increased participation in school sports teams in boys and girls may prevent declines in PA among pre-adolescents from inner-city neighborhoods. Medical Subject Headings (MeSH): cardiovascular diseases, child, ethnic groups, exercise, longitudinal studies, primary prevention, risk factors (Am J Prev Med 2002;23(2):121–128) © 2002 American Journal of Preventive Medicine

Introduction

P

hysical inactivity is a major determinant of adult morbidity1– 4 and mortality.5–7 While levels of physical activity (PA) among adults generally increased through the late 1980s,8 alarming secular

From the Public Health Directorate, Re´gie re´gionale de la sante´ et des services sociaux de Montre´al-Centre (Barnett, O’Loughlin, Paradis), Joint Departments of Epidemiology, Biostatistics and Occupational Health, McGill University (O’Loughlin, Paradis), and Division of Preventive Medicine, McGill University Health Center (Paradis), Montreal, Quebec, Canada Address correspondence and reprint requests to: Tracie A. Barnett, MSc, Research Associate, Department of Public Health, Re´gie re´gionale de la sante´ et des services sociaux de Montre´al-Centre, 1301 rue Sherbrooke Est, Montre´al, Quebec, Canada, H2L 1M3. E-mail: [email protected].

declines have been reported in the past decade, particularly among young adults.9,10 Marked secular declines are also evident among youth, with surveys showing steadily decreasing proportions meeting minimum recommended levels of PA.11–14 In addition to secular declines, steep age-related declines are apparent in both cross-sectional9,15–18 and longitudinal studies among adolescents and pre-adolescents.18 –21 While the critical period during which declines in activity begin to occur are not known,15 prospective studies document marked declines among children aged 9 to 14 years,15,20,22 but not during the preschool years.23,24 History of physical inactivity is the best predictor of future inactivity,20,24 –29 but little is known about other factors that cause decline among

Am J Prev Med 2002;23(2) 0749-3797/02/$–see front matter © 2002 American Journal of Preventive Medicine • Published by Elsevier Science Inc. PII S0749-3797(02)00464-6

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active youth, particularly during the elementary school years. These secular and age-related patterns of declining activity in youth are of considerable concern, because there is consistent evidence that PA risk categories track from childhood to adolescence24,25 and, to a lesser degree, from adolescence to adulthood.20,26 –29 Furthermore, declines in PA may be linked to recent dramatic secular increases in overweight and obesity observed in youth.30 –33 Finally, the changing sociodemographic and ethnic composition of many North American communities34 call for studies that explore PA patterns in disadvantaged and minority populations.35,36 The current study investigates causes of decline in PA among active young children living in largely multiethnic, disadvantaged communities.

Methods Data Collection Data for this study were collected in classroom questionnaires from 16 control schools participating in a 5-year, nonrandomized, controlled trial to evaluate a school-based, heart-health promotion program for elementary school children aged 9 to 12 years. Data collection procedures have been described previously.37–39 Briefly, data to evaluate the impact of the program on student smoking, dietary, and PA behavior were collected in classroom questionnaires each May/June from 1993 to 1997; analyses for this paper were completed in 2001. Sociodemographic characteristics included student’s date of birth; gender; number of household residents; language(s) spoken by the student; number of years student lived in Canada; country of birth of the student, mother, and father; and parents’ employment status. A “family origin” variable was created based on language(s) spoken by the student and the country or countries of origin of the mother, father, and student. The sample included children whose family origin was Canadian (21.3%), Central American (24.1%), European (17.4%), Asian (15.6%), Middle Eastern/North African (6.8%), South American (3.8%), and Other (11.0%). Subjects included all students aged 9 to 12 years in grades four, five, and six for whom parental consent had been obtained. Sixteen control schools were matched 2:1 to 8 intervention schools based on a composite poverty index40 and on students’ mother tongue. All schools were in the lowest quartile of the poverty index. Data were collected over a 5-year period from 80.6% of eligible students in the 16 control schools for a total of 7844 questionnaires.

Selected Measures Frequency of PA was determined in a 7-day recall adapted from the Weekly Activity Checklist.41 Only physical activities that are typically of at least moderate intensity were included. Several activities from the original checklist were replaced with popular local physical activities. The original instrument correlated with an objective activity measure (Caltrac accelerometer) at r⫽0.34, p ⬍0.01, and the estimated test–retest reliability with a 3-day interval between administrations was 0.74.41 For each of the preceding 7 days, students checked the

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physical activities they had participated in on that day from a list of 25 activities. A frequency score was computed for each student by summing the total number of activities checked across all 7 days. Based on current recommendations for a daily regimen of moderate to vigorous PA,13 students were categorized as inactive if their frequency score was six or less, which indicated that they engaged in less than one activity per day on average. Children in the upper quintile of the frequency score reported 24 or more physical activities per week and were categorized as “very active,” while active children below the upper quintile were categorized as “moderately active.” Participation in school sports teams was measured by: “Think about sports teams at school. Since school started last fall, you belonged to the school . . . cross-country ski team, basketball team, volley ball team, gymnastics team, handball team, floor hockey team, other.” Students responded “yes” or “no” to each item. “School sports teams” was categorized as “yes” if students responded “yes” to one or more items. Participation in organized sports outside school was measured in two items by: (1) “Now think about sports teams outside school. Since last summer, you belonged to a . . . basketball team, volleyball team, soccer team, gymnastics team, hockey team, football team, swimming team, baseball team, judo or karate or tai chi team, other”; and (2) “Now think about sports or dance lessons. Since last summer, you took . . . swimming lessons, downhill ski lessons, hockey school, dance or ballet lessons, skating lessons, other.” Students responded “yes” or “no” to each item. Because sports or dance lessons are often taken in the context of team activities, and because these two items were correlated (Spearman rank order correlation coefficient r⫽0.43, p ⫽0.001), we created a single “sports outside school” variable, which was categorized as “yes” if students had belonged to any team, taken any lessons, or both. Two indicators of sedentary behavior were obtained by (1) “On school days, you usually watch . . . 6 or more TV programs a day, 4 or 5 TV programs a day, 2 or 3 TV programs a day, 1 TV program a day, you don’t watch TV on school days”; and (2) “Usually you play video games like Gameboy or Nintendo . . . every day, a couple of times each week, hardly ever, never.” Perceived self-efficacy to do PA was measured in a sevenitem subscale adapted from previous research42 by: “How sure are you that you can . . . (a) do physical activities on Saturday mornings; (b) be good at physical activities; (c) do physical activities when you have lots of homework; (d) do physical activities when you arrive home late after school; (e) do physical activities when your parents want you to do something else; (f) do physical activities when it is very cold outside; and (g) do physical activities when you don’t feel like it.” Responses for each item were scored 1 (very sure), 2 (somewhat sure), or 3 (not sure), and summed to create a subscale score. The internal reliability coefficient of the PA self-efficacy subscale was 0.68. Students were categorized into either high/moderate (7 to 14) or low/very low (15 to 21). Students’ perceptions of their parents’ level of participation in physical activities was measured by: “Does your mother/father do sports or physical activity . . . often, sometimes, or rarely/never?” Students’ perceptions of their parents’ level of encouragement to practice physical activities was measured

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by: “Does your mother/father tell you to do sports or physical activity . . . often, sometimes, or rarely/never?”

Statistical Analysis All subjects from comparison schools with baseline data, who had follow-up data 1 year later, 2 years later, or both, were identified. These subjects were categorized as inactive, moderately active, or very active at baseline, and were followed up to determine activity status 1 or 2 years later. Baseline predictors of decline to an “inactive” status were identified among subjects who were initially classified as moderately or very active at baseline. One-year cohort analysis. Data were collected from a total of 3432 grade-four and grade-five students aged 9 to 12 years at baseline in May/June 1993, 1994, 1995, or 1996. One-year follow-up data were collected in May/June 1994, 1995, 1996, or 1997 from 1734 (50.5%) of the 3432 students. Observations totaled 2318: 1145 students contributed one set of observations (either from grade four to grade five, or from grade five to grade six); 554 students contributed two sets of observations (from grade four to grade five, and again from grade five to grade six); and 15 students contributed three sets of observations (due to repeated grades). Of the 2318 observations, 1873 (80.3%), including 961 boys and 912 girls, were moderately or very active at baseline, and therefore were retained for multivariate analysis. Independent predictors of 1-year decline in PA were identified using the generalized estimating equation method, which accounts for dependence between repeat observations of the same subject.43 The matrix of correlation between study years was computed using the autoregressive method. Potential predictors of decline investigated included sociodemographic characteristics (age; number of years lived in Canada; family ethnic origin; country of birth [Canada or other]; parents’ employment status; participation in school sports teams; participation in organized sports outside school; body mass index [BMI]; smoking status; and sedentary behavior [TV viewing and video game playing]. Psychosocial variables included perceived self-efficacy for PA; parental role modeling (i.e., subject’s perception of mother’s and father’s level of PA); and parental support for PA (i.e., perceived level of mother’s and father’s encouragement to practice PA). All potential predictors significant at p ⫽0.10 in univariate analyses were entered into the models; those significant at p ⬍0.10 were retained. Subsequently, all predictors not retained were entered into the models one by one to identify possible confounders to be included in the final models. Because the univariate analyses suggested that the predictors of decline might differ by sex, all analyses were performed separately for boys and girls. We also identified the 1-year predictors of remaining inactive among 445 inactive children (i.e., children who were inactive at baseline and remained inactive at follow-up were compared with children who were inactive at baseline but increased their level of activity at follow-up) using the generalized estimating equation method. We hypothesized that these predictors would differ substantively from predictors of becoming inactive among active students because declines had presumably occurred at an earlier age.

Two-year cohort analysis. Data were collected from a total of 1299 grade-four students aged 9 to 10 years at baseline in May/June 1993, 1994, or 1995. Two-year follow-up data were collected in May/June 1995, 1996, or 1997 from 639 (49.2%) of the 1299 students; 509 subjects (79.5%), including 266 boys and 243 girls, were moderately or very active at baseline and, therefore, were retained for multivariate analysis. Because no students contributed more than one set of observations in this cohort, multivariate logistic regression analysis was used to identify 2-year predictors of decline in PA. Potential predictors investigated were the same as those examined in the 1-year cohort analysis.

Results Compared to subjects lost to follow-up at 1 year, children retained for analysis were slightly younger (mean⫽10.7 years, standard deviation⫽0.9 years, and mean age⫽10.3 years, standard deviation⫽0.8 years, respectively; p ⫽0.0001); fewer lived in households with five or more 5 persons (p ⫽0.006); more were born in Canada (50.8% vs 62.6%, p ⫽0.001); more mothers (23.1% vs 29.5%, p ⫽0.001) and fathers (20.9% vs 24.3% , p ⫽0.038) were born in Canada; more mothers were employed (56.3% vs 63.7%, p ⫽0.001); and finally, more children retained for analysis reported participating in team sports at school (24.6% vs 18.7%, p ⫽0.001) or in organized sports outside school (74.8% vs 79.5%, p ⫽0.003), although fewer were “very active” (27.1% vs 24.2%, p ⫽0.08). Similar differences between children retained and those lost to follow-up were noted in the 2-year cohort analysis. Table 1 shows that the risk of being inactive at follow-up was strongly related to the baseline PA level in both boys and girls. Approximately one in ten active boys and one in five active girls became inactive at follow-up. It is notable that 48.6% to 62.3% of children who were inactive at baseline were categorized as active at follow-up.

One-Year Cohort Analysis At the 1-year follow-up, 9.4% of initially active boys and 18.8% of initially active girls reported less than one activity per day and were, therefore, considered to have declined to an inactive status. In univariate analyses, the baseline level of activity was a strong predictor of decline in both sexes: 10.9% of moderately active boys declined compared to 5.7% of very active boys (p ⫽0.013); 20.7% of moderately active girls declined compared to 10.7% of very active girls (p ⫽0.002). Grade was a predictor of decline in girls only, with grade-five girls more likely to decline than grade-four girls (21.4% vs 16.6%, p ⫽0.062). Boys born in Canada were less likely to decline (6.5% vs 14.2%, p ⫽0.001), while girls whose parents were born in Canada were less likely to decline (14.8% vs 20.5%, p ⫽0.048, and 12.9% Am J Prev Med 2002;23(2)

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Table 1. Activity levels in the 1- and 2-year cohort analyses, Montreal, Canada, 1993–1997 Follow-up activity level 1-year cohort Baseline activity level Boys All Inactive Moderately active Very active Girls All Inactive Moderately active Very active

2-year cohort

n

Inactive %

Moderately active %

Very active %

1144 183 682 279

13.8 37.7 10.9 5.7

62.2 54.1 68.9 50.9

1174 262 734 178

24.5 44.7 20.7 10.7

62.1 52.3 67.6 53.9

vs 20.9%, p ⫽0.009 for mothers and fathers, respectively). Mother’s employment status predicted decline in girls only (22.8% with unemployed mothers declined compared to 16.3% with employed mothers, p ⫽0.018). Boys who did not participate in school teams were more likely to decline (5.4% vs 10.6%, p ⫽0.021). There was no apparent relationship between TV viewing and risk of decline among boys, but the risk of decline was 21.6%, 21.1%, 17.1%, and 13.5% among girls who watched six, four to five, two to three, or zero to one TV programs per day, respectively (p ⫽0.05 for four or more vs three or fewer TV programs). Risk of decline decreased significantly as self-efficacy increased (p ⫽0.002 in boys, and p ⫽0.003 in girls). Finally, risk of decline was not associated in either boys or girls with BMI, smoking status, father’s employment status, parental modeling and support variables, video game playing, or participation in organized sports outside school. Table 2 shows the independent predictors of decline over 1 year. Moderate baseline activity and low selfefficacy were independent predictors of decline in both

n

Inactive %

Moderately active %

Very active %

24.1 8.2 20.2 43.4

322 56 199 67

17.4 44.6 13.6 6.0

61.5 42.9 67.8 58.2

21.1 12.5 18.6 35.8

13.4 3.1 11.7 35.4

317 74 188 55

28.7 51.4 25.5 9.1

59.9 43.2 64.9 65.5

11.4 5.4 9.6 25.4

sexes. Ethnicity emerged strongly in the boys’ model: Boys born outside Canada were twice as likely to decline than Canadian-born boys, and boys of Asian family origin experienced an almost twofold increase in risk of decline. Not participating in school teams also independently predicted decline among boys. Mother’s being unemployed and subject watching four or more TV programs per day were independent predictors of decline among girls only. Significant predictors of remaining inactive (compared to children who increased their levels of activity) among boys included: BMI above the 85th percentile (odds ratio [OR]⫽2.09, 95% confidence interval [CI]⫽1.02– 4.28); fathers employed (OR⫽3.46, 95% CI⫽1.19 –10.07); and mothers unemployed (OR⫽2.26, 95% CI⫽1.08 – 4.76). Grade five (OR⫽2.21, 95% CI⫽1.31–3.72); no team sports outside school (OR⫽1.76, 95% CI⫽1.00 –3.09); and father never/ sometimes encouraging PA (OR⫽2.50, 95% CI⫽1.23– 5.09) were significant predictors of remaining inactive among girls.

Table 2. Independent 1- and 2-year predictors of decline in physical activity among elementary schoolchildren, Montreal, Canada, 1993–1997 Declined to <1 activity/day at 1 year Predictor Boys (n ⫽ 961) Moderate activity Low self-efficacy Born outside Canada Asian No school teams Girls (n ⫽ 912) Moderate activity Low self-efficacy ⱖ4 TV programs/day Mother unemployed Grade 5

Declined to <1 activity/day at 2 years

OR

95% CI

Predictor

OR

95% CI

1.66 1.67 2.13 1.81 1.81

0.91–3.05 1.03–2.71 1.31–3.46 1.03–3.16 0.93–3.55

Moderate activity Born outside Canada

2.52 1.96

0.84–7.50 0.91–4.20

1.91 1.70 1.40 1.54 1.35

1.10–3.32 1.15–2.49 0.97–2.02 1.07–2.23 0.94–1.93

Moderate activity No school teams ⱖ4 TV programs/day Born outside Canada

2.75 2.14 1.93 1.85

1.01–7.49 0.92–5.00 0.99–3.74 0.96–3.55

CI, confidence interval; OR, odds ratio.

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Two-Year Cohort Analysis At the 2-year follow-up, 11.7% of initially active boys and 21.8% of initially active girls reported less than one activity per day. In univariate analyses, 13.6% of moderately active boys declined compared to 6.0% of very active boys (p ⫽0.094); among girls, these proportions were 25.5% and 9.1%, respectively (p ⫽0.009). Canadian-born subjects were less likely to decline, among both boys (9.5% vs 17.1%, p ⫽0.080) and girls (18.4% vs 28.6%, p ⫽0.071). As in the 1-year follow-up, there was a strong dose–response relationship between television viewing and risk of decline among girls: The risk of decline was 30.3%, 24.6%, 18.0%, and 7.4% among girls who watched six, four to five, two to three, or zero to one TV programs per day, respectively. Girls who had not participated in school sports teams were more likely to decline (25.1% vs 12.5%, p ⫽0.036). Risk of decline in PA over 2 years was not associated with BMI, smoking status, parental modeling or support, father’s and mother’s employment status, video game playing, or participation in organized sports outside school in either boys or girls. In multivariate analysis (Table 2), moderate activity at baseline and country of birth were independent 2-year predictors of decline in both boys and girls. No other variables were retained in the boys’ model. Among girls, not participating in school sports teams and watching four or more TV programs per day were each associated with an approximate twofold increase in risk of decline.

Secondary Analyses Because schools vary in opportunities for PA, a possible school effect on level of PA was investigated in a one-way analysis of variance (data not shown). The mean PA frequency score among students in one school was significantly different from all others in the 2-year analysis, because it contributed no cases (i.e., no students declined to less than one activity per day). After repeating the main analysis, excluding this one school, the final models remained unchanged. To define the study population of active children, the lower end of the distribution of the activity frequency score was cut off. This might have resulted in nonrandom misclassification, since children who were misclassified as inactive at baseline were not retained for further analysis, while those misclassified as active were retained. It is possible that regression to the mean resulted in overestimates of the proportion of active children declining to an inactive status, because some children who appeared to have declined in fact simply maintained low levels of activity. Indeed, one third to one half of inactive children were active at follow-up, although only 3.1% and 8.2% of inactive of girls and boys, respectively, became very active (Table 1). To

determine if misclassification affected predictors of decline, we repeated the analysis including 259 children who were inactive at baseline but active at followup, under the assumption that these children were misclassified as inactive at baseline. Results from the multivariate analyses remained unchanged, with the exception that “grade five” was replaced with “country of birth” as a predictor in the girls’ 2-year model, after controlling for baseline status of PA. In addition, the predictors of inactivity identified among those inactive at baseline suggest that the populations below and above the “active” cutoff differ appreciably. While the potential for misclassification remains, these results increase our confidence in the validity of the PA measure and, in particular, in its ability to discriminate between children according to levels of PA.

Discussion Few studies have investigated predictors of change or decline in PA in children. In one study that specifically examined decline, activity preferences and parent transporting child to activity location were important predictors, but explained only 15% and 6% of change in boys’ and girls’ activity levels, respectively.44 Four other prospective studies investigated predictors of later PA level among primary school youth20,45– 47; while length of follow-up and subsets of predictors investigated varied, one or more studies identified the following predictors of later PA behavior: baseline level of PA,20,46,47 participation in sports-club training20 or community sports,46 physical education grade,20 enjoyment of sports,46 access to sports facilities,47 self-efficacy/barriers related to PA,45,46 and parent PA/selfefficacy.45,46 Only one of the two studies investigating race or ethnicity46,47 identified this variable as a significant predictor.46 This study has identified several modifiable risk factors for PA decline, including high levels of TV viewing among girls and low participation in school sports teams in boys and girls. In addition, several other subgroups at greater risk for decline in this ethnically diverse population were identified, including boys of Asian family origin, children born outside Canada, and girls with unemployed mothers. While these latter factors are not modifiable, they do help identify groups at higher risk that could be targeted for intervention. Birth outside of Canada was a strong and consistent predictor of decline. Differences in socioeconomic status could be implicated in this relation, as has been established among adults16 and older youth.48 This finding might reflect differential opportunities to be involved in sports, rather than differences in subject characteristics.49 However, being of Asian origin was predictive of decline in boys even after adjusting for being “born outside Canada,” suggesting that, while the effect of birth country on decline may be mediated by Am J Prev Med 2002;23(2)

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the family socioeconomic status, cultural and ethnic factors are likely involved. It is possible that some cultural groups respond unfavorably when sports teams become more competitive in the higher grades, or are more willing to forfeit time devoted to free-play activities as school demands on their time increase. Clearly, more prospective studies comprising sufficient numbers of youth from different ethnic backgrounds are required in order to provide data needed to support cogent policymaking in increasingly multicultural urban environments. Lack of participation in school sports teams was predictive of decline in all children, while participation in organized sports outside school was not. Because far more students participated in organized sports outside school than in teams at school, the former may be more widely accessible to children in these communities or may be perceived as being more rewarding. While not participating in school teams may in some cases have been “forced” upon children through lack of opportunity, clearly some children who compensated for this through free play or community-based activities at baseline no longer did so at follow-up. Participating in school sports teams appears to exert a positive influence on general activity levels that extends beyond the school environment, possibly via benefits acquired through experience with interschool competition, a known predictor of future activity level.19,49 The effect of school sports teams was more “transient” in boys (i.e., predictive of 1- but not 2-year decline) and more “latent” in girls (i.e., predictive of 2but not 1-year decline). It may be that boys who do not participate in school sports teams, or who abandon them early on, nevertheless practice enough PA either through sports teams in the wider community, through free play, or both. However, fewer girls may sustain level of free play activity in the absence of structured schoolbased activity. Results of this study suggest that, at least among girls, TV viewing is associated with declines in PA. Sallis et al.44 also found a small but significant gender difference in the effect size of television viewing on PA decline. Others17,50 have reported PA and TV viewing to be more closely related in females than in males. It may be that TV viewing encroaches more on lowintensity activity or free-play activity favored by girls, rather than on team and other organized sports favored by boys.17,22 We investigated these hypotheses in secondary analyses and determined that high television viewing was an even stronger predictor of decline among girls who were not participating in any sports teams at baseline. Among girls participating in sports teams at baseline, TV viewing was a weaker, albeit significant, predictor of decline. TV viewing was also a strong predictor of “dropping” team sports among girls, suggesting that TV is eroding levels of PA through both free-play and organized sports (data not shown). 126

Previous work in this same study population determined that physical inactivity was a significant predictor of excess weight gain.39 Given the positive link between TV viewing and obesity51,52 and the results of this current analysis, one could hypothesize that PA is situated in the causal pathway between TV viewing and obesity, such that TV viewing causes physical inactivity, which in turn, causes excess weight gain. Indeed, reductions in TV-viewing hours in association with significant increases in PA have been shown to prevent or reduce obesity.53 However, reductions in obesity have also been achieved without concomitant increases in PA.54 Although the relationship among TV viewing, PA, and obesity remains equivocal among girls,55,56 our results suggest that it would be prudent to limit time spent watching TV among school-aged children.

Implications for Prevention The findings from this study are useful to prevention programs in two ways. First, intervention programs need to be tailored to specific cultural and ethnic preferences of groups, such as those born outside Canada and those of Asian origin, identified in this study as being at greater risk of PA decline. More research is required to determine to what degree background, environmental, or other factors are responsible for the strong and consistent differences in risks for decline. Second, these findings suggest that experience with school sports teams can influence the degree to which children will adhere to active lifestyles. Several schools provided little or no opportunity for children to participate in team sports. Clearly, not all children are able to compensate through communityrun team activities. Finally, the impact of television viewing on risk of decline was remarkable. Prevention efforts should inform parents and guardians that, at least among girls, regularly watching four or more TV programs on weekdays contributes significantly to a decline in level of PA.

Limitations The PA questionnaire used in this study did not measure either intensity or duration of activities. However, among pre-adolescent youth, correlates of PA vary little by level of intensity.46 The questionnaire used in this study incorporated modes of activity as memory cues, was based on a previously validated measure,41 and was field tested extensively in young subjects. Furthermore, well-known associations with PA were confirmed, providing further evidence of the validity of the measure. The use of a dichotomous dependent variable, rather than a continuous one, results in some loss of power. However, the use of the dependent variable in its dichotomized form is consistent with the research objective, which is to examine predictors of being “inactive” at follow-up. Changes in activity level where

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subjects remain sufficiently active are not relevant in this analysis. In addition, the PA measure is not sensitive enough to discriminate between small changes in PA level. However, discriminating between wide categories of activity level is possible. There was a moderately high level of attrition in the 1- and 2-year cohorts. Census data show that mobility in disadvantaged Montreal neighborhoods is high; families may move frequently for reasons related to economic circumstances. Even though selection bias may have occurred, there is little reason to suspect that the relations between decline and the potential independent predictors differed between subjects lost to follow-up and those retained for analysis.

10.

11. 12. 13.

14.

15.

Conclusion This is the first prospective study to investigate a wide range of potential predictors of decline in levels of PA in an initially active, pre-adolescent population. The results strongly support the implementation of school sports teams that are accessible and appealing to students of diverse ethnic backgrounds, as well as restrictions on hours spent watching TV, at least during elementary school years, in order to prevent declines in levels of PA. This research was conducted as part of the Projet que´ becois de de´ monstration en sante´ du coeur, which was financed by the National Health Research and Development Program, Health Canada (grant 66053754-H), the Quebec Ministry of Health and Social Services, and the Quebec Heart and Stroke Foundation. Tracie Barnett is a Medical Research Council Doctoral Award recipient. Jennifer O’Loughlin was a National Health Research Scholar during the time this study was conducted and is currently a Chercheur-Boursier of the Fonds de la recherche en sante´ du Que´ bec.

16. 17.

18. 19.

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American Journal of Preventive Medicine, Volume 23, Number 2