Does Participation in Organized Sports Predict Future Physical Activity for Adolescents from Diverse Economic Backgrounds?
Article Outline
- Abstract
- Methods
- Results
- Discussion
- Acknowledgments
- References
- Copyright
Abstract
Purpose
To examine cross-sectional and longitudinal associations between socioeconomic status (SES), gender, sports participation and moderate-to-vigorous physical activity (MVPA) in adolescents.
Methods
Project EAT (Eating Among Teens), a population-based longitudinal study followed a socioeconomically and ethnically diverse sample of 1709 adolescents in 1998–1999 (Time 1) and 2003–2004 (Time 2). Mixed model regression analyses were used to examine longitudinal trends in MVPA as a function of SES and previous sports involvement.
Results
For both genders, participation in organized sports and weekly hours of MVPA were positively associated with SES. On average, MVPA decreased between high school and young adulthood for both genders. Adolescents who participated in sports during high school showed a steeper decline in weekly hours of MVPA than their non–sports-participating counterparts. SES had a significant moderating effect on the change in MVPA over time for boys who participated in organized sports, with low SES boys showing a steeper decline in MVPA between time periods than higher SES boys. Although on average, a statistically significant difference in MVPA between previous sports participants and nonparticipants remained at Time 2, for all SES groups and both genders, the gap between hours of MVPA was either overcome or significantly narrowed by young adulthood.
Conclusions
Increased dependence on organized sports for MVPA may be insufficient to meet the needs of youth following high school, especially for low SES youth. Designing physical activity promotions that reach and address the unique needs of lower SES youth and families is a public health priority.
Keywords: Adolescents and young adults, Organized sports, Physical activity, SES disparities
Emerging scientific consensus indicates that physical activity is important for the health of adolescents [1]. Health problems associated with low levels of physical activity during adolescence include type 2 diabetes [2], increased symptoms of depression [3], increased risk of adult sedentary behavior [4], and obesity [5]. The prevalence of adolescent obesity has increased dramatically over the past several decades across all socioeconomic (SES) strata, and data suggest that risk for adolescent obesity is inversely associated with SES [6]. A better understanding of associations among SES, gender, and physical activity level over time is important for identifying which subgroups of youth are at particularly high risk of inadequate physical activity. Such information is critical for developing tailored obesity prevention and physical activity interventions that will best meet the needs of all youth.
Multiple population-based studies have shown that adolescent participation in physical activity declines sharply as youth age, with a widening gender gap [7]. The 2003 Youth Risk Behavior Surveillance System survey (YRBSS) estimated that the percentage of high school girls in the United States who participate in sufficient vigorous physical activity declined from 64% in 9th grade to 46% in 12th grade. For boys, the percentage declined from 73% to 64% throughout high school [8]. The health consequences associated with inadequate physical activity make it imperative to determine what contributes to adolescent physical activity behavior and to identify factors associated with sustaining adequate physical activity into adulthood.
One of the short-term benefits of participation in organized sports is that it helps adolescents to achieve daily recommended amounts of physical activity [9]. Furthermore, participation in organized sports has generally been found to be associated with lower use of cigarettes and marijuana use, although has also been found to be associated with greater alcohol use [10]. Organized sports are distinguishable from unstructured activity in that they usually require at least one of the following: adult organization, supervision, transportation, field and gym space, money, and/or time devoted outside of school hours. Participation in physical activity and sports has been shown to promote physical and mental health, academic achievement, and skills such as teamwork, self-discipline, and leadership [5]. However, low SES youth may be disadvantaged with regard to their ability to participate in organized sports because of financial and logistical barriers that they and their families face [11].
In a cross-sectional study involving more than 50,000 students in 9th grade, participants in organized sports were three times more likely than nonparticipants to be physically active [12]. Pfeiffer et al determined that female sports participants in 8th and 9th grade were one and a half times more likely to be active in 12th grade than nonparticipants [13]. However, there is a paucity of research determining whether the decline in physical activity after leaving the school environment is significantly different among adolescents who participated in organized sports during high school, as compared with the change found among non–sport-participating adolescents. Although short-term benefits of organized sports have been well researched, questions remain about the long-term benefits; specifically, whether participation in organized sports as an adolescent predicts higher rates of moderate-to-vigorous physical activity (MVPA) as a young adult.
Given concerns about barriers to adequate physical activity for low SES adolescents and unclear relationships between school-age participation in organized sports and future physical activity in young adulthood, the aims of the current study are twofold: (1) to examine cross-sectional associations between SES, sports participation, and MVPA in adolescent boys and girls, and (2) to examine whether organized sports participation during adolescence is associated with MVPA during young adulthood 5 years later and whether these associations differ across gender and SES.
Methods
Study population
Data are from population-based, longitudinal studies Project EAT (Eating Among Teens)–I and Project EAT-II, which examined dietary intake, physical activity, and weight status among young people [14]. The sample consisted of 1639 young adults (45% male) who completed survey assessments at baseline and follow-up. At baseline the mean age of participants was 15.9 years (SD = .8 year); at follow-up, the mean was 20.4 years (SD = .8 year). In Project EAT-I, 3138 high school students in Minnesota schools completed in-class surveys and anthropometric measures during the 1998–1999 academic year (Time 1). Five years later (2003–2004; Time 2), as the students progressed to late adolescence/young adulthood, Project EAT-II aimed to resurvey by mail all original participants for whom contact information was available. Follow-up survey data were collected from 68% of those contacted (n = 1710), representing 56% of the original high school cohort. The University of Minnesota's Institutional Review Board Human Subjects Committee approved all study protocols used in Project EAT-I and -II.
Measures
Sports participationIn this study, 10th grade students were asked, “During the past 12 months, on how many sports teams did you play?” Choices included no teams, one team, two teams, and three or more teams [15]. Adolescents were characterized as sports participants if they participated in one or more teams and as non–sports participants if they participated on 0 teams. This measure was only assessed during high school (Time 1). In young adulthood (Time 2), young adults were not asked about sports participation at Time 2, because after high school, sports participation is more uncommon.
Moderate to vigorous physical activityQuestions related to physical activity were adapted specifically from the widely used Godin Leisure-Time Exercise Questionnaire [16]. These two survey items individually assessed moderate to vigorous activity (MVPA) by asking, “In a usual week, how many hours do you spend doing the following activities …” Vigorous activity was described as strenuous, during which the heart beats rapidly, whereas moderate activity was described as not exhausting. More than 10 examples of specific activities were given after each question. Possible responses ranged from 0 to ≥ 6 hours per week. Test-retest correlations for strenuous- and moderate-intensity PA were .63 and .52, respectively [17]. The responses (0, <.5, .5–2, 2.5–4, 4.5–6, >6 hours per week) were re-coded to the midpoint of each range (0, 0.3, 1.3, 3.3, 5.3, and 8 hours per week) and summed to create a score that represented total time spent in MVPA.
Sociodemographic characteristicsGender, age, and SES were based on self-report at Time 1. The primary determinant of SES was parental educational level, defined by the higher level of either parent [18]. Other variables used to assess SES included family eligibility for public assistance (response options: yes/no/don't know), eligibility for free or reduced-cost school meals (yes/no/don't know), and maternal and paternal employment status (full-time/part-time/not working/don't know). An algorithm was developed using the ideas of Classification and Regression Trees in which a missing variable is replaced by a correlated surrogate variable [19]. Algorithmic classification scores were reduced by two levels if the family was receiving public assistance, and by one if the youth was eligible for free or reduced-cost school meals, or had two unemployed parents. Validity is supported by parental assessment of SES in a substudy of 902 parents in which 876 provided information of parental education and work status, as well as family income. Correlations between parent and student-reported measures of SES were .67 (Spearman correlation) and .79 (weighted kappa).
Statistical analysis
Analyses examined whether the following held true: (1) participation in team sports during high school varied with respect to SES at Time 1, (2) weekly hours of MVPA varied with respect to SES at both time points, (3) participation in team sports during high school was associated with weekly hours of MVPA at Time 1, (4) longitudinal trends in the level of MVPA varied as a function of previous sports involvement, (5) longitudinal trends in the level of MVPA varied by SES, and (6) there was an interaction effect of SES and previous sports involvement on longitudinal trends in MVPA. The interaction examines whether the longitudinal trends in MVPA for those who participate in sports versus those who do not are the same or different across different SES groups. Longitudinal trends were estimated and tested using participants with available MVPA data at both time points. Mixed model regressions were used to estimate and test differences in MVPA across time and included a random effect for individuals to account for longitudinal correlation. Depending on which research question was being examined, the mixed model regression included a main effect for year (1999 or 2004), five SES categories (low, middle–low, middle, middle–high, and high), a dichotomous indicator of sports involvement, and appropriate interactions between year, SES, and sports involvement. All p values are based on t tests from regression analysis. All regression analyses were adjusted for race and stratified by gender. The SAS program version 9.1 (SAS Institute, Cary, NC) was used for all analyses.
Because attrition in the study population did not occur completely at random, the data were weighted using the response propensity method [20], in which the inverse of the estimated probability that an individual responded at Time 2 was used as the weight. These procedures are described in detail elsewhere [21]. The weighted sample has a similar demographic make-up to the original Project EAT-I sample. The weighted race/ethnicity and SES percentages of the study sample are as follows: 59.5% white, 16.8% Asian, 13.3% African-American, and 10.4% mixed or other race; SES was 17.8% low, 18.9% low middle, 26.6% middle, 23.3% upper middle, and 13.3% high. Concern regarding the missing-at-random assumption used by the propensity-weighting method was lessened by the finding that after weighting, there were no significant differences between the baseline MVPA or organized sports participation of respondents and nonrespondents for Project EAT-II.
Results
Cross-sectional analyses
Cross-sectional associations between SES and sports participationAt Time 1, participation in organized sports during high school was positively associated with SES for both males and female in analyses adjusted for race. Each SES level in both boys and girls showed an incremental increase in organized sports participation (53–80% in boys and 30–71% in girls; Figure 1). The test for linear trend was significant for both genders (p < .001).
Figure 1
Percentage of high school adolescents participating in organized sports (time 1), stratified by gender.
Similarly, MVPA was positively associated with SES. Controlling for race, on average, higher SES males and females reported more hours of MVPA during both high school and young adulthood (overall SES trend in boys, p = .048; in girls, p < .001; Table 1). For example, during high school high SES girls reported 8.0 hours (SD = 4.1) of MVPA per week as compared with 5.8 hours (SD = 4.5) of MVPA for low SES girls.
Table 1. Moderate-to-vigorous physical activity (MVPA) at Time 1 (high school) and Time 2 (young adulthood) stratified by socioeconomic status (SES) and sport participation
| Sports participation | No sports participation | |||
|---|---|---|---|---|
| Time 1 | Time 2 | Time 1 | Time 2 | |
| Boys | n = 505 | n = 228 | ||
 Low | 7.4 ± 5.5 | 6.9 ± 6.7 | 4.9 ± 4.4 | 5.1 ± 5.2 |
| Low middle | 9.6 ± 4.4 | 6.9 ± 5.6 | 4.4 ± 4.2 | 5.7 ± 5.3 |
| Middle | 8.1 ± 4.7 | 7.0 ± 5.1 | 4.5 ± 4.0 | 5.0 ± 4.0 |
| Upper middle | 8.7 ± 4.4 | 6.8 ± 4.3 | 6.1 ± 4.4 | 4.9 ± 3.5 |
| High | 9.8 ± 3.8 | 7.7 ± 4.0 | 5.2 ± 4.0 | 7.7 ± 4.2 |
| Total | 8.7 ± 4.5 | 7.0 ± 4.8 | 5.0 ± 4.3 | 5.3 ± 4.4 |
| Girls | n = 521 | n = 385 | ||
| Low | 5.8 ± 4.5 | 2.6 ± 2.7 | 4.2 ± 4.8 | 3.5 ± 3.8 |
| Low middle | 5.9 ± 4.7 | 3.5 ± 3.4 | 4.4 ± 4.9 | 3.8 ± 4.5 |
| Middle | 6.8 ± 4.3 | 4.5 ± 3.7 | 4.1 ± 4.0 | 4.0 ± 3.6 |
| Upper middle | 7.6 ± 4.2 | 4.9 ± 3.5 | 3.4 ± 2.7 | 2.8 ± 2.7 |
| High | 8.0 ± 4.1 | 5.3 ± 3.2 | 5.0 ± 3.5 | 3.9 ± 3.6 |
| Total | 7.0 ± 4.4 | 4.4 ± 3.5 | 4.2 ± 4.1 | 3.4 ± 3.7 |
For both boys and girls, sports participation during high school was positively associated with higher levels of MVPA during high school (p < .001). The mean number of weekly hours of MVPA during high school for sports-involved boys was 8.7 hours (SD = 4.5) compared with 5.0 (SD = 4.3) for non–sports involved boys (p <.001; Table 1 and Figure 2). Similarly, for sports-involved girls in high school, the mean number of weekly MVPA hours was 7.0 (SD = 4.4) compared with 4.2 (SD = 4.1) for non–sports involved girls (p < .001; Table 1 and Figure 2).
Figure 2
Longitudinal change in reported weekly MVPA (hours) between high school (time 1) and young adulthood (time 2) by reported organized sports participation at time 1.
Longitudinal analysis findings
Longitudinal change in MVPA change stratified by SESOverall, adolescents reported a decreased number of mean hours spent in weekly MVPA between high school and young adulthood. The change in MVPA over time was not statistically different for different SES groups for either sex (time by SES interaction p = .08 for males and .58 for females).
Longitudinal change in MVPA stratified by sports participationOverall, adolescents reported a decreased number of mean hours spent in weekly MVPA between high school and young adulthood (Table 1). However, the change in MVPA over time was different according to their organized sports participation during high school (time by sports participation interaction, p <.001 for both males and females). For males who did not participate in organized sports during high school, weekly MVPA did not significantly change after finishing high school (5.0 hours in high school vs. 5.3 hours as young adults, p = .284; Figure 2). In contrast, males who did participate in sports during high school reported a decline in MVPA by 1.7 hours per week (8.7 hours in high school vs. 7.0 hours per week as young adult, p < .001; Figure 2). For females who did not participate in organized sports, weekly MVPA declined by .8 hour after completing high school (4.2 hours in high school vs. 3.4 hours as young adults, p < .001; Figure 2). In contrast, females who did participate in sports reported a larger decline in PA, averaging 2.6 hours per week (7.0 hours in high school vs. 4.4 hours as young adults, 0 <.001; Figure 2). Although the gap in hours of MVPA between adolescents who previously participated in organized sports and those who did not previously participate in organized sports significantly narrowed at Time 2, a statistically significant difference of 1.7 hours for boys (p < .001) and 1.0 hours for girls (p < .05) remained at Time 2.
MVPA change over time stratified by sports participation and SESSES had a small but significant moderating effect on the change in MVPA over time for boys who participated in organized sports in high school versus boys who did not (p = .011 for the three-way interaction between time period, SES, and sports participation). Lower SES boys (particularly low middle SES boys) who participated in organized sports in high school showed a steeper decline between time periods than the higher SES boys who participated in organized sports in high school (Figure 3). There was a 2.6 hour per week decrease (from 9.6 hours to 7.0 hours) for low-middle SES sports-participating boys compared with a 2.1 hour perweek decrease (from 9.8 to 7.7 hours) for high SES sports participating boys (p = .019 for comparison between low–middle and high SES boys; Figure 3). Furthermore, unlike the other SES groups, the highest SES males who did not participate in organized sports during high school greatly increased their total MVPA in young adulthood to a level no different from the young adult MVPA of their sports participating counterparts (Figure 3). SES did not have a statistically significant moderating effect on the change in MVPA over time for females (Figure 4).
Figure 3
Males: Average weekly hours of MVPA change between high school (time 1) and young adulthood (time 2) stratified by SES. Solid lines represent adolescents who participated in organized sports at time 1, dashed lines represent nonparticipants.
Figure 4
Females: Average weekly hours of MVPA change between high school (time 1) and young adulthood (time 2) stratified by SES. Solid lines represent adolescents who participated in organized sports at time 1, dashed lines represent nonparticipants.
Discussion
For both boys and girls, participation in organized sports during high school was positively associated with SES. Furthermore, higher SES females and males reported more hours of MVPA during both high school and young adulthood regardless of sports participation category. Hours spent in MVPA decreased between high school and young adulthood for all groups except non–sports-participating boys. Adolescents who participated in sports during high school showed a steeper decline in weekly hours of MVPA than their non–sports-participating counterparts. SES had a small but significant moderating effect on the change in MVPA over time for boys who participated in organized sports versus boys who did not, indicating that the gap in MVPA remained larger for low SES compared with higher SES boys. Although subjects who participated in organized sports during high school (Time 1) did have, on average, higher weekly hours of MVPA in young adulthood (Time 2), for all SES groups and both genders, the gap between hours of MVPA for sports participants and nonparticipants was either overcome or significantly narrowed by young adulthood.
We found significant SES disparities in both organized sports involvement during high school (Time 1) and level of physical activity at both time points. SES appears to play a major role in which groups of youth experience organized sports, with lower SES adolescents at a significant disadvantage. In addition to the fees and equipment required for young persons to participate in organized sports, low SES youth may face other barriers to participation [11]. Low SES parents may be less available to transport their children to practices and games, adolescents may be required to either help in the home or generate income from an after-school job, or these adolescents may lack the role modeling and support that may be present in higher SES families.
Similar to previous studies [13], [22], [23], [24], [25], [26], our data show that high school organized sports participation was associated with higher hours of future MVPA. Most of these studies were conducted in Scandinavian countries, where organized sports may differ from those in the United States. The one study conducted in the United States examined school age females up to age 18 [13]. In contrast, our data describe patterns through young adulthood and includes both males and females. Sports participants in our study showed a steep decline in their weekly MVPA once high school was complete. Although during organized sports participation, the MVPA gap between participants and nonparticipants was large, this gap had significantly narrowed 5 years later. Organized sports participation is noticeably important during adolescence, as those in sports are more active than those who are not. However, the behavior and skills learned in organized sports may not persist into adulthood. Our data show SES has a moderating effect, particularly for boys, in the way MVPA changes over time. Although most SES groups for both genders showed some long-term benefit of previous sports participation in terms of higher young adulthood MVPA, for lower SES boys, sports participation in high school was not as protective of future MVPA hours as it was for their higher SES peers. Although the retention of MVPA behavior learned from sports participation appears to be minimal in most young adults, the even smaller influence upon low SES boys is troubling.
Strengths of the current study are the use of a large, ethnically and economically diverse sample and the longitudinal research design. To the best of our knowledge, this is the first study using a U.S. sample that examined the effect of sports participation during adolescence on future physical activity during young adulthood. The specific SES measures allowed us to stratify by SES, which is an important factor in designing interventions to overcome inaccessibility of many youth physical activity options. Limitations of the study include potential bias in physical activity measure because of self-reporting and lack of information on sports involvement at Time 2. Our study essentially treats all Time 2 youth as “previous” organized sports participants but does not identify those young adults who may still be participating in college or other level organized sports from those who have stopped organized sports all together. The brevity of the MVPA assessment tool may also affect interpretation of findings. It is possible that our tool underestimates the level of MVPA done “on the job,” and there may be differences across SES in the amounts of MVPA done in the work setting by young adults. In addition, the 5 years following high school is a period of much transition. Some young adults will continue on to college and others will start families, with varying environmental and social factors influencing amount of physical activity. We cannot conclude from this study whether changes in MVPA seen in this period will necessarily persist throughout adulthood or whether the gap in MVPA between previous sports participants and nonparticipants will narrow or widen over time.
Implications for future research
Longitudinal studies tracking organized sports participation beyond school age youth and well into adulthood could help clarify what role both current and historical organized sports participation plays in adult MVPA. Although the short term benefits of organized sports participation are clear, future research can help clarify both type and duration of long-term benefits; specifically whether previous sports participants remain more physically active than nonparticipants for a lifetime or whether the gap between them disappears. Data collected on Finnish youth showed that adolescents who participated in individual endurance sports (cross-country running, skiing, swimming) were more likely to be physically active as adults than those youth who had participated in nonendurance sports or who had never participated in sports [22]. Analysis of sports or activity type in a diverse US population would be helpful in identifying which activities are most likely to become “lifelong” for Americans. More exploration is needed to determine what attributes and programs engage youth in lifetime MVPA. Qualitative data collected from physically active young adults may help determine when and how physical activity became part of their identity, especially for youth who are active outside of organized sports. Data to explore barriers to low SES sports and MVPA participation would help clarify reasons for disparities. Such information could help in the design of interventions intended to sustain physical activity for a lifetime, not just during school years. Development of such programs is especially critical for low SES youth and adults.
Implications for future practice and policy
Because the retention of MVPA behavior from high school sports participation appears minimal, especially for low SES boys, organized sports as they are currently practiced may be an inadequate means of encouraging lifetime MVPA. Enhancing organized sports messages to ensure lifetime physical activity may help to alleviate the decline in young adult MVPA by previous organized sports participants. Many youth organizations are already advocating for change regarding structure of youth PA and decreased dependence on organized activities for exercise [27]. The American Academy of Pediatrics has issued the following position statement: “Organized sports programs for preadolescents should complement, not replace, the regular physical activity that is a part of free play, child-organized games, recreational sports, and physical education programs in the schools. Regular physical activity should be encouraged for all children whether they participate in organized sports or not” [28].
Although the AAP position targets preadolescents, low activity rates of adolescents and findings from the current study support strategies for enhancing MVPA both within and outside of organized sports. Health care providers can advise parents of children and adolescents to encourage unstructured play, serve as role models for being physically active during every day activity, and promote lifelong and/or individual sports as opposed to just team sports. School physical education programs should provide adolescents with the support and skills to engage in activities suitable for an ongoing active lifestyle. Public health interventions targeting youth and high school coaches could provide support and formal training about the importance of teaching lifelong exercise skills. Communities should strive to provide resources to make physical activity accessible to all. Supported by growing evidence about economic disparities, and questionable sustainability of physical activity after organized sports participation has ceased, increasing access to programs making physical activity an easy choice designed to last a lifetime should be a public health priority.
Acknowledgments
This study was developed when the principal author was a fellow at the University of Minnesota, and was supported by grant R40-MC00310 (PI: Neumark-Sztainer) from the Maternal and Child Health Bureau (Title V, Social Security Act), Health Resources and Services Administration, Department of Health and Human Services, and by the Adolescent Health Protection Research Training grant number T01-DP000112 (PI: Bearinger) from the Centers for Disease Control and Prevention, Department of Health and Human Services and by the Leadership Education in Adolescent Health (PI: Singh); DHHS, HRSA Grant # T71-MC-00006.
References
- Evidence based physical activity for school-age youth. J Pediatr. 2005;146:732–737
- Prevalence and trends in overweight among US children and adolescents, 1999–2000. JAMA. 2002;288:1728–1732
- Naturally occurring changes in physical activity are inversely related to depressive symptoms during early adolescence. Psychosom Med. 2004;66:336–342
- Prediction of physical activity and physical work capacity (PWC150) in young adulthood from childhood and adolescence with consideration of parental measures. Am J Hum Biol. 2001;13:190–196
- . Healthy People 2010: Understanding and improving health. 2nd ed.. Washington, DC: US Department of Health and Human Services; 2000;
- . Epidemic increase in childhood overweight, 1986–1998. JAMA. 2001;286:2845–2848
- Decline in physical activity in black girls and white girls during adolescence. N Engl J Med. 2002;347:709–715
- Youth risk behavior surveillance—United States, 2003. MMWR Surveill Summ. 2004;53:1–96
- . Leisure-time physical activity behavior: Structured and unstructured choices according to sex, age, and level of physical activity. Int J Behav Med. 2002;9:111–121
- . Sports and physical activity participation and substance use among adolescents. J Adolesc Health. 2005;36:486–493
- Barriers to physical activity: Qualitative data on caregiver-daughter perceptions and practices. Am J Prev Med. 2004;27:218–223
- . Differences in behavior, psychological factors, and environmental factors associated with participation in school sports and other activities in adolescence. J Sch Health. 2003;73:113–120
- Sports participation and physical activity in adolescent females across a four-year period. J Adolesc Health. 2006;39:523–529
- Obesity, disordered eating, and eating disorders in a longitudinal study of adolescents: How do dieters fare 5 years later?. J Am Diet Assoc. 2006;106:559–568
- Reliability of the Youth Risk Behavior Survey Questionnaire. Am J Epidemiol. 1995;141:575–580
- . A simple method to assess exercise behavior in the community. Can J Appl Sports Sci. 1985;10:141–146
- Parental correlates of physical activity in a racially/ethnically diverse adolescent sample. J Adolesc Health. 2002;30:253–261
- . The measurement of social class in health studies: Old measures and new formulations. IARC Sci Publ. 1997;138:51–64
- . Classification and Regression Trees. Belmont, CA: Wadsworth; 1984;
- . Survey nonresponse adjustments for estimates of means. Int Stat Rev. 1986;54:137–139
- Overweight status and weight control behaviors in adolescents: Longitudinal and secular trends from 1999 to 2004. Prev Med. 2006;43:52–59
- Adolescent participation in sports and adult physical activity. Am J Prev Med. 2003;24:22–28
- Physical activity in childhood and adolescence as predictor of physical activity in young adulthood. Am J Prev Med. 1997;13:317–323
- A longitudinal study of youth sports participation and adherence to sports in adulthood. Int J Sociol Sports. 1997;32:373
- . The process of socialization into keep-fit activities. Scand J Sports Sci. 1986;8:89–97
- . Factors explaining the physical activity of young adults: the importance of early socialization. Scand J Med Sci Sports. 1999;9:120–127
- Effects of a mass media campaign to increase physical activity among children: Year-1 results of the VERB campaign. Pediatrics. 2005;116:e277–e284
- Organized sports for children and preadolescents. Pediatrics. 2001;107:1459–1462
PII: S1054-139X(08)00353-4
doi:10.1016/j.jadohealth.2008.08.011
© 2009 Society for Adolescent Medicine. Published by Elsevier Inc. All rights reserved.
