A hidden Markov modeling approach combining objective measure of activity and subjective measure of self-reported sleep to estimate the sleep-wake cycle.

Characterizing the sleep-wake cycle in adolescents is an important prerequisite to better understand the association of abnormal sleep patterns with subsequent clinical and behavioral outcomes. The aim of this research was to develop hidden Markov models (HMM) that incorporate both objective (actigraphy) and subjective (sleep log) measures to estimate the sleep-wake cycle using data from the NEXT longitudinal study, a large population-based cohort study. The model was estimated with a negative binomial distribution for the activity counts (1-minute epochs) to account for overdispersion relative to a Poisson process. Furthermore, self-reported measures were dichotomized (for each one-minute interval) and subject to misclassification. We assumed that the unobserved sleep-wake cycle follows a two-state Markov chain with transitional probabilities varying according to a circadian rhythm. Maximum-likelihood estimation using a backward-forward algorithm was applied to fit the longitudinal data on a subject by subject basis. The algorithm was used to reconstruct the sleep-wake cycle from sequences of self-reported sleep and activity data. Furthermore, we conduct simulations to examine the properties of this approach under different observational patterns including both complete and partially observed measurements on each individual.

Shared and distinct parental influences on teen impaired driving in rural and suburban contexts: A mixed methods study of young drivers.

OBJECTIVE: To explore shared and distinct parental influences on rural and suburban adolescents' riding with an impaired driver (RWI) and driving while impaired (DWI) behaviors during high school. METHODS: Participants in the NEXT Generation Health Study (NEXT) were classified into four RWI/DWI trajectory classes (i.e., Abstainer, Escalator, Decliner, Persister) which described patterns of RWI/DWI from high school to emerging adulthood. A follow-up, in-depth, qualitative interview was conducted with a purposeful selection of participants from each trajectory class between March and September 2020. Guided by Ecodevelopmental Theory, the interview included questions which explored parent-teen influences on driving and RWI/DWI. RESULTS: Imposition of a curfew was a shared parental influence in rural and suburban contexts. Unique to the rural context, parent modeling of RWI/DWI was described as normative and occurring since childhood. CONCLUSIONS: Prevention interventions targeting parent RWI/DWI may reduce their children's risk for RWI/DWI among rural adolescents.

Longitudinal perspectives of riding with a cannabis-impaired driver.

OBJECTIVE: To explore decisions and perceptions of engaging in riding with a cannabis-impaired driver (RWI) during high school and young adulthood to build context around RWI-cannabis events. METHODS: Participants were sampled from the NEXT Generation Health Study (NEXT), a 7-year national cohort study of adolescent health behaviors. Four RWI and driving while impaired (DWI) trajectories classes (i.e., Abstainer, Escalator, Decliner, Persister) were previously derived.A theoretical model based on ecological systems theory guidedin-depth semi-structured interviews to includecomplex, social-developmental and environmental multi-level factors affectingpersonal experiences with RWI-cannabis during high school, after high school, and during young adulthood. Participants (n = 105) were purposively selected from each trajectory class for follow-up, in-depth, qualitative interviews. All interviews were conducted via Zoom between March and September 2020. RESULTS: Two unique themes emerged as facilitators of RWI-cannabis: "Driving Context" and "Trust in Driver". "Legal Concerns" and "Concerns with Safety Emerge with Age" were themes that described deterrents to RWI-cannabis. CONCLUSIONS: Current data suggest that youth RWI-cannabis occurs during daytime hours and while driving to everyday activities. Youth report legal concerns as a potential deterrent to RWI-cannabis in high school and concerns for safety emerge in young adulthood. The multifaceted nature of RWI-cannabis among young drivers identifies potential complexities for programming designed to reduce RWI/DWI-cannabis.

The impact of ActiGraph's low-frequency extension filter on measurement of children's physical activity.

This study examines differences in accelerometer-based measurements of children's movement with and without applying ActiGraph's low-frequency extension (LFE) filter. Thirty children wore ActiGraph GT9X devices during structured physical activity (PA) periods. Raw accelerometry data for each activity period were processed with and without the LFE filter applied. For each activity period, paired t-tests were used to compare vector magnitude counts and minutes spent in moderate-to-vigorous physical activity (MVPA) with and without the LFE filter applied. Repeated measures MANOVA models were used for compositional data analysis of the percentage of time spent in sedentary behaviour and light, moderate, and vigorous PA with and without the LFE filter applied. Applying the LFE filter significantly increased vector magnitude counts and estimated minutes spent in MVPA for all activity periods when compared to the normal filter. For brisk walking, the LFE filter had a significant impact on the composition of time spent in sedentary behaviour and PA intensities. Children's activity data processed with the LFE filter may not be compatible with cut-points for activity levels developed with the normal filter, and caution should be taken when comparing children's activity levels or movement data between studies that do and do not use the LFE filter.

Trajectories and Outcomes of Adolescents that Ride With an Impaired Driver/Drive While Impaired.

Introduction: For young drivers, independent transportation has been noted to offer them opportunities that can be beneficial as they enter early adulthood. However, those that choose to engage in riding with an impaired driver (RWI) and drive while impaired (DWI) over time can face negative consequences reducing such opportunities. This study examined the prospective association of identified longitudinal trajectory classes among adolescents that RWI and DWI with their later health, education, and employment in emerging adulthood. Methods: We analyzed all seven annual assessments (Waves, W1-W7) of the NEXT Generation Health Study, a nationally representative longitudinal study starting with 10th grade (2009-2010 school year). Using all seven waves, trajectory classes were identified by latent class analysis with RWI (last 12 months) and DWI (last 30 days) dichotomized as ≥once = 1 vs. none = 0. Results: Four RWI trajectories and four DWI trajectories were identified: abstainer, escalator, decliner, and persister. For RWI and DWI trajectories respectively, 45.0% (N=647) and 76.2% (N=1,657) were abstainers, 15.6% (N=226) and 14.2% (N=337) were escalators, 25.0% (N=352) and 5.4% (N=99) were decliners, and 14.4% (N=197) and 3.8% (N=83) persisters. RWI trajectories were associated with W7 health status (χ2=13,20, p<.01) and education attainment (χ2=18.37, p<.01). Adolescent RWI abstainers reported better later health status than RWI escalators, decliners, and persisters; and decliners reported less favorable later education attainment than abstainers, escalators, and persisters. DWI trajectories showed no association with health status, education attainment, or employment. Conclusions: Our findings suggest the importance of later health outcomes of adolescent RWI. The mixed findings point to the need for more detailed understanding of contextual and time-dependent trajectory outcomes among adolescents engaging in RWI and DWI.

Mapping the complex causal mechanisms of drinking and driving behaviors among adolescents and young adults.

BACKGROUND: The proportion of motor vehicle crash fatalities involving alcohol-impaired drivers declined substantially between 1982 and 1997, but progress stopped after 1997. The systemic complexity of alcohol-impaired driving contributes to the persistence of this problem. This study aims to identify and map key feedback mechanisms that affect alcohol-impaired driving among adolescents and young adults in the U.S. METHODS: We apply the system dynamics approach to the problem of alcohol-impaired driving and bring a feedback perspective for understanding drivers and inhibitors of the problem. The causal loop diagram (i.e., map of dynamic hypotheses about the structure of the system producing observed behaviors over time) developed in this study is based on the output of two group model building sessions conducted with multidisciplinary subject-matter experts bolstered with extensive literature review. RESULTS: The causal loop diagram depicts diverse influences on youth impaired driving including parents, peers, policies, law enforcement, and the alcohol industry. Embedded in these feedback loops are the physical flow of youth between the categories of abstainers, drinkers who do not drive after drinking, and drinkers who drive after drinking. We identify key inertial factors, discuss how delay and feedback processes affect observed behaviors over time, and suggest strategies to reduce youth impaired driving. CONCLUSION: This review presents the first causal loop diagram of alcohol-impaired driving among adolescents and it is a vital first step toward quantitative simulation modeling of the problem. Through continued research, this model could provide a powerful tool for understanding the systemic complexity of impaired driving among adolescents, and identifying effective prevention practices and policies to reduce youth impaired driving.

Autonomous motivation and action planning are longitudinally associated with physical activity during adolescence and early adulthood.

We examined the associations of autonomous motivation, controlled motivation, and physical activity (PA) planning with PA participation over six years across the adolescent-to-adult transition. Participants from the NEXT Generation Health Study, a nationally representative cohort study of U.S. 10th graders (N=2785), completed surveys yearly from 2010 to 2016 (four years post-high school). This study used data from Waves 2 (W2) through 7 (W7). Data were analyzed using growth models accounting for the complex survey design and controlling for sex, race/ethnicity, and body mass index. A piecewise growth model with two pieces (Piece 1: W2-W4; Piece 2: W4-W7) indicated that PA declined during late adolescence (W2-W4) (b=-0.31, ß=-0.22, p<.001), but did not decline after the transition into early adulthood (W4-W7) (b=-0.08, ß=-0.04, p=.052). Autonomous motivation was positively associated with PA at all waves (b=0.23-0.33, ß=1.90-4.37, p<.001). Controlled motivation was only positively associated with PA at W3 (12th grade) (b=0.13, ß=1.54, p=.011). PA planning varied significantly between individuals and significantly predicted PA (b=0.44, ß=0.21, p<.001). Although PA decreased significantly during late adolescence, PA did not decrease significantly after transitioning into early adulthood (one to four years post-high school). Elevated autonomous motivation and PA planning were consistently and significantly associated with higher PA, suggesting that these may be useful intervention targets during this adolescent-to-adult transition.

Riding with an impaired driver and driving while impaired among adolescents: Longitudinal trajectories and their characteristics.

PURPOSE: The purpose of this study was to identify and characterize trajectory classes of adolescents who ride with an impaired driver (RWI) and drive while impaired (DWI). METHODS: We analyzed all 7 annual assessments (Waves W1-W7) of the NEXT Generation Health Study, a nationally representative longitudinal study starting with 10th grade (2009-2010 school year). Using all 7 waves, latent class analysis was used to identify trajectory classes with dichotomized RWI (last 12 months) and DWI (last 30 days; once or more = 1 vs. none = 0). Covariates were race/ethnicity, sex, parent education, urbanicity, and family affluence. RESULTS: Four RWI trajectories and 4 DWI trajectories were identified: abstainer, escalator, decliner, and persister. For RWI and DWI trajectories respectively, 45.0% (n = 647) and 76.2% (n = 1,657) were abstainers, 15.6% (n = 226) and 14.2% (n = 337) were escalators, 25.0% (n = 352) and 5.4% (n = 99) were decliners, and 14.4% (n = 197) and 3.8% (n = 83) persisters. Race/ethnicity (χ2 = 23.93, P = .004) was significantly associated with the RWI trajectory classes. Race/ethnicity (χ2 = 20.55, P = .02), sex (χ2 = 13.89, P = .003), parent highest education (χ2 = 12.49, P = .05), urbanicity (χ2 = 9.66, P = .02), and family affluence (χ2 = 12.88, P = .05) were significantly associated with DWI trajectory classes. CONCLUSIONS: Among adolescents transitioning into emerging adulthood, race/ethnicity is a common factor associated with RWI and DWI longitudinal trajectories. Our results suggest that adolescent RWI and DWI are complex behaviors warranting further detailed investigation of the respective trajectory classes. Our study findings can inform the tailoring of prevention and intervention efforts aimed at preventing illness/injury and preserving future opportunities for adolescents to thrive in emerging adulthood.

Validation of a continuous measure of cardiometabolic risk among adolescents.

OBJECTIVES: We validated a continuous cardiometabolic risk (CMR) measure among adolescents. METHODS: Five metabolic syndrome (MetS) components including waist circumference, triglycerides, high-density lipoprotein cholesterol, fasting blood glucose, and mean arterial pressure were assessed in a national cohort of U.S. adolescents (n=560; 16.5 ± 0.5 y/o at baseline) in 10th grade (2010, Wave 1 (W1)), and follow-up assessments four (W4) and seven (W7) years later. Separately by wave, linear regressions were fitted to each MetS component controlling for age, sex, and race/ethnicity, and yielded standardized residuals (Z-scores). Wave-specific component Z-scores were summed to obtain composite CMR Z-scores. Four- and seven-year CMR change (CMR-diff W1-W4 and W1-W7). and average CMR risk (CMR-avg; (W1 + W4)/2 and (W1 + W7)/2) were calculated using the CMR Z-scores. W7 MetS was determined using adult criteria. Student's t-test and receiver operating characteristic (ROC) curve were conducted. RESULTS: Participants meeting the adult criteria for MetS at W7 (74 of 416, 17.8%) had statistically significant (p<0.01) higher values for W1 CMR Z-scores (0.92 vs. -0.21), W4 CMR Z-scores (1.69 vs. -0.28), W7 CMR Z-scores (2.21 vs. -0.55), W1-W4 CMR-avg (1.53 vs. -0.27), W1-W7 CMR-diff (1.29 vs. -0.21), and W1-W7 CMR-avg (1.46 vs. -0.48) than those not meeting MetS criteria. Most results were similar for males and females in the sex-stratified analyses. The areas under the ROC curve were 0.61, 0.71, and 0.75 for W1, W4 and W7 Z-scores. CONCLUSIONS: Findings support the validity of the continuous CMR Z-scores calculated using linear regression in evaluating and monitoring CMR profiles from adolescence to early adulthood.

Physical Activity and Enjoyment in Parent-Child Dyads During Shared Physical Activity.

Purpose: The purpose of this study was to compare objectively-measured physical activity (PA) and enjoyment of five shared PAs in parent-child dyads. Method: Thirty-one parent-child dyads (mean±SD; age, parents: 38.0 ± 6.6 years, children: 5.9 ± 1.7 years) completed separate PA sessions, which included five standardized PAs (brisk walking, jumping games, dancing, body-weight exercises, and tag games) in random order for each dyad. Parent and child moderate-to-vigorous PA (MVPA) and accelerometer counts per minute (CPM) were measured using Actigraph GT9X activity monitors. The Visual Analog Scale was used to assess enjoyment of children and parents. Repeated measures ANOVAs and paired t-tests determined differences in PA within and between children and parents for the activities, respectively. Friedman Tests with post hoc Wilcoxon signed-rank tests determined significant differences in enjoyment across the activities for children and parents and Wilcoxon signed-rank tests compared enjoyment between children and parents for each PA. Results: Jumping games resulted in the highest proportion of time spent in MVPA and highest overall CPM for children and parents (p < .05). Compared to parents, children spent proportionally more time in MVPA during jumping games, body-weight exercises, and tag games (all, p < .05). Tag games were the most enjoyable PA for children and parents (p < .05). Children enjoyed body-weight exercises more than parents (p < .05). Conclusions: Future indoor PA programs and research interventions that include parent-child dyads should consider implementing jumping games, body-weight exercises, and tag games during shared PA, which resulted in higher MVPA and enjoyment by both children and parents when compared to walking and dancing.

The Effects of Varying Structured Physical Activity Duration on Young Children's and Parents' Activity Levels.

Purpose: The purpose of this study was to examine whether structured physical activity (PA) in a family-based community exercise program affects PA of young children and parents. Method: Twenty-two children (mean ± SD; age, 4.9 ± 2.1 years) and their parents (age, 34.3 ± 7.6 years) participated in unstructured PA sessions followed by either short- or long-duration structured PA sessions, while wearing an ActiGraph GT9X activity monitor on their right hip to estimate PA. Independent t-tests compared children's and parents' PA during short- and long-structured PA sessions. Paired t-tests compared short- versus long-structured PA sessions. A mixed model ANOVA compared PA during unstructured versus structured sessions and between children and parents. Results: Children spent proportionately more time in moderate-to-vigorous PA (MVPA) and had higher accelerometer counts/min than parents during short-structured PA (children:60.9 ± 18.8% vs. parents:17.7 ± 6.8%, children:3870 ± 742 vs. parents:1836 ± 556 counts/min, p < .05) and long-structured PA (children:61.1 ± 20.1% vs. parents:12.6 ± 4.9%, children:3415 ± 758 vs. parents:1604 ± 633 counts/min, p < .05). No statistical differences were found between short- and long-structured PA sessions for proportion of time spent in MVPA or counts/min for children or parents (all, p > .05). Children spent proportionally more time in MVPA and had higher counts/min during unstructured PA compared to structured PA (unstructured MVPA:54.4 ± 3.9% vs. structured MVPA:38.2 ± 4.2%, unstructured counts/min:3830 ± 222 vs. structured counts/min:2768 ± 239 counts/min; p < .05). Conclusions: Children were more active than parents during both the unstructured and structured PA sessions. However, unstructured PA sessions resulted in 63-77% and 10-11% of PA recommendations for children and adults, respectively. Family-based exercise programming can provide an opportunity for children and their parents to attain MVPA during the week.

Accuracy of Self-Reported Height, Weight, and BMI Over Time in Emerging Adults.

INTRODUCTION: Self-reported height and weight may lead to inaccurate estimates of associations between BMI and health indicators. The purpose of this study is to assess anthropometric misreporting in emerging adults, compare weight classification by self-reported and direct measures, and examine associations of self-reported and direct measures with cardiometabolic biomarkers. METHODS: Self-reported and directly measured height and weight were obtained in five waves of a nationally representative cohort study of U.S. tenth graders (n=2,785) conducted in 2010-2016; data were analyzed in 2018. Cardiometabolic biomarkers were assessed in three waves in a systematically recruited subsample (n=567). Pearson correlations (r) and Lin's concordance correlations (ρc) evaluated misreporting. Gwet agreement coefficient-1 evaluated weight classification agreement by self-reported and direct measures. Generalized estimating equations examined associations of cardiometabolic biomarkers with self-reported and direct measures. RESULTS: Participants overreported height by 1.0-1.7 cm and underestimated weight by 0.6-1.7 kg. Self-reported BMI was 0.6-1.0 lower than measured. Self-reported and measured height, weight, and BMI were strongly correlated (r=0.88-0.97, 0.86-0.98, and 0.65-0.96, respectively) and concordant (ρc=0.82-0.96, 0.94-0.97, and 0.65-0.95, respectively). Agreement of weight classification by self-reported and direct measures ranged from Gwet agreement coefficient-1=0.79-0.94. Associations of ten cardiometabolic biomarkers with self-reported BMI, measured BMI, and waist circumference were similar in magnitude, direction, and precision. CONCLUSIONS: Self-reported and measured BMI were strongly correlated and concordant, providing substantial to near-perfect agreement in weight classification. Findings suggest self-reported BMI in U.S. emerging adults provides nearly identical estimates of associations with cardiometabolic biomarkers.

Association between the Built Environment and Active Transportation among U.S. Adolescents.

INTRODUCTION: As a major determinant of obesity and cardiovascular disease in the United States, decreasing physical activity (PA) has led researchers to study factors influencing daily PA. One opportunity for modifying PA is in relation to transportation to and from school and/or work. We examined the association between characteristics of the built environment of home neighborhoods and transportation-related PA to school or work among youth and emerging adults. METHODS: The data were drawn from Waves 1 and 4 of the NEXT Generation Health Study (n=2780), a nationally representative, longitudinal cohort study starting with 10th grade (Wave 1) in the 2009-2010 school year. Modes of travel to/from school were categorized into three groups: those using active transportation (walking/cycling), public transportation, and passive transportation (being driven or chauffeured/driving). Neighborhood characteristics included land use mix, street connectivity, residence density, park density, recreational density, and walkability. Multinomial logistic regressions and one-way ANOVAs were used to examine multivariate associations between modes of travel to and from work/school and neighborhood characteristics. Analysis accounted for complex survey features including stratification, clustering and sampling weights. RESULTS: After controlling for covariates (i.e., ethnicity, sex, education, and socioeconomic status), more land use diversity, street connectivity, residence density, and walkability were significantly correlated with active transportation in both waves and more park and recreational density were significantly correlated with active transportation in Wave 1, compared with passive transportation. CONCLUSIONS: More mixed land use, greater connected streets as well as higher walkability and density of residence, parks and recreational facilities were associated with active transportation; suggesting city planning officials may consider creating more walkable and liveable communities to promote daily transportation-related PA.

Beyond Sleep Duration: Bidirectional Associations Among Chronotype, Social Jetlag, and Drinking Behaviors in a Longitudinal Sample of US High School Students.

Inadequate sleep and problematic drinking are prevalent among high school students and are significant public health issues. Inadequate sleep may contribute to alcohol use through impairments in emotion regulation or cognitive functioning, whereas alcohol use may lead to inadequate sleep through the biological effects of alcohol or social influences. However, the directionality of the associations between sleep and drinking variables remains unclear as most prior studies were cross-sectional. This study utilizes longitudinal data from the NEXT Generation Health Study to examine bidirectional associations between alcohol use and sleep adequacy in a nationally representative sample across 3 years of high school. Students reported usual bedtimes and waketimes for scheduled- and free-days, alcohol use, and heavy episodic drinking. Estimates of sleep duration, chronotype, and social jetlag were calculated. Cross-lagged autoregressive models revealed evidence of alcohol use predicting subsequent sleep duration and timing, and sleep timing predicting subsequent alcohol use. Specifically, previous-wave alcohol use predicted shorter free-day sleep duration and later chronotype at 11th and 12th grade, and more social jetlag at 12th grade; similar results were obtained for heavy episodic drinking. Eleventh grade social jetlag predicted subsequent year current alcohol use; eleventh grade chronotype and social jetlag predicted subsequent year heavy episodic drinking. Bidirectional findings suggest that alcohol use and sleep may reflect mutually reinforcing life style choices. Understanding these bidirectional associations could inform risk prevention interventions. Given the implications of poor sleep for adolescents, further research on possible social influences on the alcohol-sleep relations is merited. Clinical Trial Registration: NCT01031160.

Diet quality of US adolescents during the transition to adulthood: changes and predictors.

Background: Influences on diet quality during the transition from adolescence to adulthood are understudied.Objective: This study examined association of 3 diet-quality indicators-Healthy Eating Index-2010 (HEI), Whole Plant Foods Density (WPF), and Empty Calories (EC; the percentage of calories from discretionary solid fat, added sugar and alcohol)-with lifestyle behaviors, baseline weight status, and sociodemographic characteristics in US emerging adults.Design: Data come from the first 4 waves (annual assessments) of the NEXT Plus Study, a population-based cohort of 10th graders enrolled in 2010 (n = 566). At each assessment, participants completed 3 nonconsecutive 24-h diet recalls, wore accelerometers for 7 d, and self-reported meal practices and sedentary behaviors. Self-reported sociodemographic characteristics were ascertained at baseline. Generalized estimating equations examined associations of time-varying diet quality with baseline weight status and sociodemographic characteristics and time-varying lifestyle behaviors.Results: Diet quality improved modestly from baseline (mean ± SE: HEI, 44.07 ± 0.53; WPF, 1.24 ± 0.04; and EC, 35.66 ± 0.55) to wave 4 for WPF (1.44 ± 0.05, P < 0.001) and EC (33.47 ± 0.52, P < 0.001), but not HEI (45.22 ± 0.60). In longitudinal analyses, higher HEI and lower EC scores were observed in Hispanic compared with white participants. Better diet quality was associated with greater moderate-to-vigorous physical activity, more frequent breakfast and family meals, less frequent fast food and meals during television viewing, and shorter durations of television viewing, gaming, and online social networking. Diet-quality indicators were not consistently associated with time-varying physical inactivity, baseline weight status, or sociodemographic characteristics.Conclusions: Diet quality of emerging adults in the US remained suboptimal, but some aspects improved marginally over the 4-y study period. Meal contexts and sedentary behaviors may represent important intervention targets. There is substantial room for improvement in diet quality in all sociodemographic subgroups. This trial was registered at clinicaltrials.gov as NCT01031160.

Changes in Moderate-to-Vigorous Physical Activity Among Older Adolescents.

OBJECTIVES: Examined patterns and determinants of objectively measured moderate-to-vigorous physical activity (MVPA) over 4 years in US emerging adults. METHODS: Waves 1 through 4 (W1 [10th grade] to W4 data of a national cohort starting in 2010 (N = 561; 16.19 ± 0.51 years) were used. MVPA was assessed annually from accelerometers; BMI calculated from measured height/weight; and surveys ascertained self-reported physical activity (PA) planning, peer PA , family support, W1 sociodemographics, W4 school status, W4 residence, and W4 employment. Latent growth modeling estimated trajectories in log-transformed duration (minutes/day) of MVPA and associations with covariates. RESULTS: Less than 9% of participants met the recommended 60+ minutes/day MVPA across W1 through W4. W1 MVPA was greater in males versus females (B = 0.46, P < .001) and Hispanic versus White (B = 0.34, P < .001) participants. Increased BMI change (W1 to W4 slope) was associated with decreased MVPA. MVPA was positively associated with PA planning (W1-W3: B = 0.10, B = 0.06, B = 0.08, Ps < .05), but not with peer PA or family support. Participants attending 4-year college versus not-attending school (B = 0.52, P < .001), and college students living on campus versus at home (B = 0.37, P < .001) were more likely to engage in MVPA at W4. Weekend MVPA remained relatively constant from W1 through W4. CONCLUSIONS: High-school students engaged in little MVPA and maintained this low level through the transition to adulthood. Emerging adults' MVPA engagement may vary according to social contexts. Those with high BMI may benefit most from interventions to promote MVPA.

Individual, social, and environmental influences on the transitions in physical activity among emerging adults.

BACKGROUND: Youth's physical activity (PA) may change across developmental periods. Although previous studies have observed a decline in levels of PA during adolescence, few studies have explored trends in PA during the transition from adolescence to young adulthood and what factors may impact the transitional change. The purpose of this study was to examine changes and predictors of change over time in PA from 10(th) grade to post-high school. METHODS: The NEXT Generation Health Study recruited a nationally-representative cohort of US 10(th)-graders, and administered longitudinal surveys in four waves (years) to follow up the participants to their first year after high school. Using transition models, the self-reported outcomes, moderate-to-vigorous PA (MVPA) and vigorous PA (VPA) each of which was repeatedly measured by one question, were modelled in association with wave-4 environmental-status variables and time-varying covariates. RESULTS: There was a continuous decline in the proportion of respondents who met or exceeded the minimum recommended level for either MVPA (from 55.97 to 34.33 %) or VPA (from 65.96 to 54.90 %) from W1 to W4. Higher scores of peer PA, family support and VPA planning were prospectively associated with higher likelihood of meeting the MVPA/VPA recommendations. At wave 4, compared to those not working, attending 4-year colleges, or living on campus, participants working full/part time, not attending school or attending community-college level schools, and living at home or in own place were more likely to engage in MVPA. CONCLUSIONS: Peer PA, family support, self-regulatory skills, and environmental status after high school are critical factors that can promote MVPA/VPA among adolescents and emerging adults.

Assessment of adolescent weight status: Similarities and differences between CDC, IOTF, and WHO references.

OBJECTIVE: The research sought to determine the reliability of assessing adolescents' weight status based on three standard criteria, Centers for Disease Control and Prevention (CDC) growth charts, International Obesity Task Force (IOTF) standards, and the World Health Organization (WHO) growth references. METHODS: Data from the NEXT Generation Health Study US 10th grade cohort (n=2323, mean age=16.19years) starting in 2009 were used. Kappa statistics assessed agreement of assignment to weight categories. Associations of weight status with perceived body image, weight control intention, and general health were examined using linear regressions accounting for complex survey design. RESULTS: Kappas across weight status criteria were≥.89 and agreement exceeded 90% in all analyses. For all three criteria, overweight and obese participants, compared to normal weight, were significantly more likely to indicate fatter body image, higher weight control intention, and poorer general health; small differences in the regression coefficients by classification method were observed. CONCLUSION: The three criteria of weight status classifications substantially agreed. Associations of weight status with selected health correlates were similar regardless of the methods. Thus, the three classifications can be considered comparable for most research and practice purposes.

Dynamic Patterns of Adolescent Substance Use: Results From a Nationally Representative Sample of High School Students.

OBJECTIVE: Use of tobacco, alcohol, marijuana, and other drugs increases during the high school years, yet little is known about individual patterns over time, particularly patterns of contemporaneous multiple-substance use. This study examined trajectories of contemporaneous substance use and how individual and social factors differentially predict patterns of substance use. METHOD: Longitudinal trajectories of substance use were examined in a nationally representative sample of students (N = 2,512) over a 3-year period (10th through 12th grades) using latent class analysis. Individual, parental, and peer risk factors in 10th grade were examined in relation to membership in trajectory classes. RESULT: A five-class model was identified: nonusers (45.5%); tobacco, alcohol, and other drug users (9.2%); alcohol and other drug users (9.2%); increasing multiple-substance users (16.7%); and decreasing multiple-substance users (19.4%). Depressive symptoms at baseline were associated with a higher likelihood of membership in all classes except the increasing multiple-substance-user class, but the association becomes insignificant when social influence factors were adjusted. Parental-monitoring knowledge was associated with a lower likelihood of membership in all classes except increasing multiple-substance-user class, whereas perceived parental disapproval was associated with a lower likelihood of membership in the tobacco, alcohol, and other drug user class. Peer substance use was associated with a higher likelihood of membership in each of the substance use classes. CONCLUSIONS: The identified longitudinal profiles highlight the pervasiveness and dynamic patterns of contemporaneous multiple-substance use during 10th through 12th grades. Negative peer influence increased risk, whereas positive parenting behaviors decreased risk. The findings are consistent with the need to foster social influences and protective factors against adolescent substance use.