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School's out … now what? Objective estimates of afterschool sedentary time and physical activity from childhood to adolescence
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Original research
School’s out . . . now what? Objective estimates of afterschool sedentary time and physical activity from childhood to adolescence Eric E. Wickel a,∗ , Sarahjane Belton b a b
University of Tulsa, College of Health Sciences, USA Dublin City University, School of Health and Human Performance, Ireland
a r t i c l e
i n f o
Article history: Received 27 March 2015 Received in revised form 27 August 2015 Accepted 17 September 2015 Available online xxx Keywords: Accelerometer Moderate-to-vigorous physical activity Sedentary time Youth
a b s t r a c t Objectives: To describe the change in afterschool levels of sedentary time and physical activity from childhood to adolescence. Design: Longitudinal. Methods: 375 youth (50% boys) from the Study of Early Child Care and Youth Development (United States) provided accelerometer data at 9 (2000/01) and 15 yrs (2006/07). Average time spent in sedentary, light, moderate, vigorous, and moderate-to-vigorous physical activity (MVPA; min h−1 ) was reported across the afterschool period (15:00–22:00) and separately across whole days. Mean comparisons were conducted to report between- and within-group differences in afterschool data. Analysis of covariance was used to determine the effect of sex, ethnicity, and baseline body mass index (BMI) on the 6-yr change in afterschool sedentary time and MVPA before and after adjusting for covariates (baseline afterschool sedentary/MVPA time, change in non-afterschool sedentary/MVPA time, difference in afterschool wear time, and socioeconomic status). Results: From 9 to 15 yrs, sedentary time increased and activity decreased during the afterschool period. After covariate adjustment, the decline in afterschool MVPA was significantly greater among girls, compared to boys (B coefficient (95%CI) = −0.94 (−1.47, −0.40)), and among overweight/obese youth, compared to youth with normal BMI values (B coefficient (95%CI) = −0.65 (−1.22, −0.08)). Conclusions: During the transition from childhood to adolescence, afterschool activity (min h−1 ) decreases while sedentary time increases. Programs are needed throughout this period that promote the maintenance of activity or encourage additional activity with age. © 2015 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
1. Introduction Daily physical activity is associated with several health benefits.1 As such, it is recommended that youth accumulate at least 60 min of moderate-to-vigorous physical activity (MVPA) each day.2 On weekdays, active opportunities exist within the school environment in the form of recess, physical education, and active classrooms. Although few youth appear to meet specific MVPA recommendations for recess3 or physical education,4 many accumulate 30 min of MVPA while at school,4 which is the recommended amount.5 In order to reach the daily MVPA guideline, participating in activity outside the timetabled school day is necessary for the majority of youth. In contrast to the structured school environment, the hours after school are relatively more discretionary. During this time,
∗ Corresponding author. E-mail address: [email protected] (E.E. Wickel).
youth participate in a range of active and sedentary behaviors,6 many of which are related to demographic, interpersonal, and environmental factors.7 Many studies examining afterschool hours utilize cross-sectional designs8 where the intent is to characterize time allocation and identify potential targets for intervention. As a result, though it has been shown that the afterschool period is an important contributor to overall MVPA in youth,9 relatively little is known about the transition in afterschool activity from childhood to adolescence. Among the few available studies, one10 reported a decrease in moderate-to-vigorous behaviors from 9 to 11 yrs, while another11 reported a decrease in moderate and vigorous activity among young (5–6 yrs at baseline) and old (10–12 yrs at baseline) cohorts over 3 and 5 yrs. Although both studies reveal a decline in afterschool activity with increasing age, the influence of sex, body size, and ethnicity (which are important biological correlates of daily activity12 ) on this transition is relatively unknown. Understanding the influence of these biological factors during the transition between childhood and adolescence is important for the design of targeted interventions aimed at modifying levels of
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Please cite this article in press as: Wickel EE, Belton S. School’s out . . . now what? Objective estimates of afterschool sedentary time and physical activity from childhood to adolescence. J Sci Med Sport (2015), http://dx.doi.org/10.1016/j.jsams.2015.09.001
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sedentary time and physical activity. Accordingly, the primary aim of this study was to describe the impact of biological factors (sex, body size, and ethnicity) on afterschool levels of sedentary time and physical activity from childhood to adolescence. Moreover, as a secondary aim, this study describes the tracking of afterschool sedentary time and physical activity. Given that few longitudinal studies exist to describe the transition in afterschool time allocation, this study addresses a key gap in the literature.
2. Methods Data for this analysis came from the Study of Early Child Care and Youth Development (SECCYD), a multi-phased prospective study of 1,364 families spanning from birth to 15 yrs. The primarily goal of the SECCYD was to examine the influence of early child care experiences on social, emotional, and physical outcomes during childhood and into adolescence. Details regarding the recruitment and consent process have been thoroughly described13 and are also available from the study’s website (http://www. nichd.nih.gov/research/supported/seccyd/pages/overview.aspx). The SECCYD research protocol was approved by each participating university’s ethics committee (University of Arkansas; University of California; University of Kansas; University of New Hampshire/Wellesley; Pennsylvania State University/University of Pittsburgh; Temple University; University of Virginia; University of Washington; Western Carolina Center; and University of Wisconsin) and written informed consent was obtained from all participating families at the onset of the study. As the study continued, verbal or implied assent was obtained from the participating child. SECCYD data were collected using subjective and objective assessment tools during four phases (Phase I: birth to 3 yrs (1991–1994); Phase II: 54 months through 1st grade (1995–1999); Phase III: 2nd through 6th grade (2000–2004); and Phase IV: 7th through 9th grade (2005–2007)). To specifically explore the transition in afterschool sedentary time and physical activity from childhood to adolescence, we examined data from Phases I (1991), III (2000/01), and IV (2006/07). Sex and ethnicity were recorded at birth. Chronological age (yrs) was determined based on the observation date (Phases III/IV) and the birth date of the participating child. Height and weight collected during Phases III/IV were used to calculate the body mass index (BMI = kg/m2 ) and BMI z-scores. Sex- and age-specific BMI percentiles14 were used to categorize youth as normal (<85th percentile) or overweight/obese (≥85th percentile). The income:needs ratio was viewed as an index of socioeconomic status (SES) and was determined from parent-reported income (including governmental assistance) and corresponding poverty thresholds defined by the United States Census Bureau.15 Physical activity was measured across a 7-day period with the Actigraph 7164 in Phase III (mean age: 9 yrs) and the Actigraph GT1 M in Phase IV (mean age: 15 yrs) (ActiGraph, Fort Walton Beach, FL, USA) using a 60-s epoch. High inter-unit classification agreement (96%) exists across varying intensities16 ; therefore the impact of using different monitors to assess sedentary time and physical activity was likely minimal in the current study. Baseline accelerometer data were primarily collected from March to May (70%), while follow-up data were primarily collected from either March to May (41%) or August to November (30%). Weekday accelerometer data from both phases were processed using ActiLife 6.4.5 from 07:00 to 22:00 (whole day) and separately from 15:00 to 22:00 (afterschool). Although it’s possible that some youth accumulated additional activity after 22:00, the amount is likely low given that typical bed times for youth17 approximate this hour. Implausible data were operationally defined as activity counts·min−1 ≥ 20,00018 and were replaced with zero. Non-wear
time was identified as periods of 60 consecutive zero counts with an allowance of two interruptions during this 60-min period.19 Wear time was reported across the whole day and during afterschool hours by removing total daily and afterschool non-wear time, respectively. Youth providing valid whole day and afterschool data on ≥3 weekdays at 9 and 15 yrs were included in the analysis. Weekdays were considered valid if whole day accelerometer wear time ≥10 h day−1 and afterschool wear time ≥4 h day−1 . Accelerometer data were processed using activity count min−1 thresholds for sedentary (≤100), light (>100 and <2296), moderate (≥2296 and <4012), vigorous (≥4012), and MVPA (≥2296).20,21 Summary statistics (min h−1 and min day−1 ) were calculated at 9 and 15 yrs for the whole day and during afterschool hours. These values were used to report the percent contribution of each category to whole day and afterschool levels. Descriptive statistics were computed for the entire sample, and separately for girls and boys. Group differences were examined using t (independent and dependent) and chi-square tests, while analysis of covariance (ANCOVA) was used to determine the effect of sex, ethnicity (Caucasian, non-Caucasian), and baseline BMI (normal, overweight/obese) on the change in afterschool sedentary and MVPA time (min h−1 ) from childhood to adolescence. Covariates considered for inclusion were baseline afterschool sedentary and MVPA (min h−1 ), change in non-afterschool sedentary and MVPA (min h−1 ), change in accelerometer wear time (min day−1 ), and SES. Models were conducted before and after covariate adjustment and were performed separately for sedentary and MVPA. Nearly 40% of the total sample provided baseline and follow-up accelerometer data within the same season. No significant mean difference was observed in the change in afterschool sedentary time or MVPA between those with data from the same season or those with data from different seasons, therefore the effect of season was not included in the model. Additional analyses using sex-specific quartiles of afterschool MVPA and sedentary time (min h−1 ) were conducted to report the percentage of youth remaining ≤25th (lowest) and > 75th (highest) quartiles at 9 and 15 yrs. The highest quartile reflects greater accumulated levels of sedentary and MVPA; therefore, stability within this quartile would be desirable for MVPA but not for sedentary time. Odds ratios (OR (95% CI)), obtained via binary regression, were calculated to report the likelihood of maintaining membership within a specified quartile and were viewed as an index of tracking. Odds ratios were adjusted for ethnicity, baseline BMI z-score, baseline SES, and the difference in accelerometer wear time (min day−1 ). SPSS 20 was used for data analyses and significance was set at p ≤ 0.05.
3. Results Of the 947 youth who provided at least a single valid day of accelerometer data, a total of 375 (50% boys; 80% Caucasian) met the inclusion criteria at 9 and 15 yrs and were included in the current study. Chi-square analyses did not reveal a difference between excluded and included participants due to sex (2 (1) = 0.27, p = 0.61) or ethnicity (2 (1) = 0.53, p = 0.47); however, excluded participants had higher baseline SES values compared to included participants (4.5 vs 3.8; p = 0.003). Typical wear time during the afterschool period approximated 6 h (86% of the defined afterschool period). Baseline and follow-up descriptive and afterschool data are shown in Table 1, arranged by sex. Sedentary time and light intensity activity contributed the highest proportion of afterschool time at baseline and follow-up, approximating ≥90%. In general, the contribution from MVPA was higher among boys, compared to girls, at both time periods, but significantly declined with increasing age in both groups. Much of the transition in afterschool time allocation over the 6-yr period was attributable to changes
Please cite this article in press as: Wickel EE, Belton S. School’s out . . . now what? Objective estimates of afterschool sedentary time and physical activity from childhood to adolescence. J Sci Med Sport (2015), http://dx.doi.org/10.1016/j.jsams.2015.09.001
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Table 1 Descriptive and afterschool accelerometer data from baseline to follow-up. Girls (n = 190)
Boys (n = 185) Baseline
Follow-up
Mean change (95% CI)
9.1 (0.3) 18.6 (3.8) 0.64 (1.0) 4.0 (3.4)
15.1 (0.2) 22.8 (4.9) 0.56 (1.0) 5.3 (7.2)
6.0 (6.0, 6.1)b 4.3 (3.8, 4.7)b −0.08 (−0.19, 0.03) 1.3 (0.4, 2.1)b
Contributing percentage of afterschool time. Values are % (SD) Sedentary 37.2 (9.2) 61.3 (10.4) 24.2 (22.6, 25.8)b Light 55.0 (7.3)a 35.4 (9.2) −19.6 (−21.0, −18.3)b Moderate 5.4 (2.5)a 2.3 (2.3)a −3.1 (−3.6, −2.7)b Vigorous 2.4 (2.0)a 1.0 (1.5)a −1.4 (−1.7, −1.1)b MVPA 7.8 (4.2)a 3.3 (3.4)a −4.5 (−5.2, −3.8)b
37.4 (9.4) 52.5 (7.6) 6.7 (3.1) 3.4 (2.7) 10.1 (5.2)
60.8 (11.6) 33.9 (9.0) 3.4 (2.7) 1.9 (2.7) 5.3 (4.7)
23.4 (21.5, 25.2)b −18.6 (−20.1, −17.1)b −3.3 (−3.8, −2.7)b −1.5 (−2.0, −1.0)b −4.8 (−5.7, −3.9)b
Standardized afterschool time. Values are min h−1 (SD) 22.3 (5.5) 36.8 (6.3) Sedentary Light 33.0 (4.4)a 21.2 (5.5) Moderate 3.3 (1.5)a 1.4 (1.4)a a Vigorous 1.4 (1.2) 0.6 (0.9)a MVPA 4.7 (2.5)a 2.0 (2.0)a
22.5 (5.6) 31.5 (4.5) 4.0 (1.9) 2.0 (1.6) 6.0 (3.1)
36.5 (7.0) 20.3 (5.4) 2.1 (1.6) 1.1 (1.6) 3.2 (2.8)
14.0 (12.9, 15.1)b −11.2 (−12.0, −10.3)b −2.0 (−2.3, −1.6)b −0.9 (−1.2, −0.6)b −2.9 (−3.4, −2.3)b
Age BMI BMI z-score SES
a b
Baseline
Follow-up
Mean change (95% CI)
9.0 (0.3) 18.2 (3.2) 0.51 (0.9) 3.8 (2.7)
15.1 (0.1) 23.2 (4.6) 0.61 (0.8) 4.5 (3.6)
6.1 (6.0, 6.1)b 5.0 (4.6, 5.4)b 0.10 (0.01, 0.19)b 0.75 (0.40, 1.10)b
14.5 (13.5, 15.5)b −11.8 (−12.6, −11.0)b −1.9 (−2.1, −1.6)b −0.8 (−1.0, −0.7)b −2.7 (−3.1, −2.3)b
Significant gender difference (p ≤ 0.05). Significant difference between baseline and follow-up (p ≤ 0.05).
in sedentary time and light intensity activity (Table 1). A relatively lower amount of change was observed in afterschool MVPA from 9 to 15 yrs. At baseline and follow-up, daily wear time approximated 13 h and, in general, the contribution of afterschool MVPA to daily MVPA remained relatively consistent in girls (55% at 9 yrs; 48% at 15 yrs) and boys (51% at 9 yrs; 53% at 15 yrs). Unstandardized (B) coefficients (95% CI) describing the change in afterschool sedentary and MVPA time (min h−1 ) across biological factors (reference category for sex (boys), BMI (normal), and ethnicity (non-Caucasians)) are shown in Table 2. In general, the change in sedentary time was similar between girls and boys and between normal and overweight/obese youth. The unadjusted B coefficient for ethnicity was positive and significant (B = 2.96 (1.15, 4.76)), indicating a greater increase in afterschool sedentary time among Caucasians, compared to non-Caucasians, from 9 to 15 yrs. The B coefficient for ethnicity decreased after including covariates (adjusted B = 2.37 (0.73, 4.02)), but remained significant. In regards to MVPA, significant B coefficients were revealed for sex (adjusted B = −0.94 (−1.47, −0.40); p ≤ 0.001)) and BMI (adjusted B = −0.65 (−1.22, −0.08); p ≤ 0.05) indicating a greater 6-yr reduction in afterschool MVPA among girls (compared to boys) and overweight/obese youth (compared to normal weight youth). Although mean MVPA levels declined with increasing chronological age in girls and boys, the adjusted B coefficients across sex × BMI categories indicate a statistically smaller decline among normal weight boys compared to all remaining categories. This particular finding suggests the difference in MVPA decline over the 6-yr period approximated 11 min (1.56 × afterschool duration (i.e., 7 h) = 10.9 min) between normal weight boys and overweight/obese girls. In comparison to normal weight boys, the decline in MVPA among overweight/obese boys and normal weight girls was greater by 5–6 min. Sex-specific quartiles of afterschool sedentary and MVPA were analyzed to report the percentage of youth remaining in the lowest (≤25th percentile) and highest (≥75th percentile) quartiles at 9 and 15 yrs. In general, percentile values for sedentary time (min h−1 ) were similar between girls and boys, and increased from 9 yrs (girls: 25th (18.8), 75th (25.6); boys: 25th (18.4), 75th (25.9)) to 15 yrs (girls: 25th (32.5), 75th (41.0); boys: 25th (33.1), 75th (40.6)). In contrast, percentile values for MVPA (min h−1 ) were slightly lower among girls, compared to boys, and decreased from 9 yrs (girls: 25th (2.7), 75th (5.9); boys: 25th (3.5), 75th (8.2)) to 15 yrs (girls: 25th (0.7), 75th (2.6); boys: 25th (1.2), 75th (4.5)). Relatively few (≤10%)
girls or boys maintained quartile position (≤25th or >75th) for sedentary or MVPA at 9 and 15 yrs. Overall, the odds of maintaining membership in the lowest quartile for sedentary (OR (95%CI) = 3.9 (1.6, 9.4)) and highest quartile for MVPA (OR (95%CI) = 2.8 (1.2, 6.7)) were significant among boys, but not girls. However, the findings also revealed increased odds of maintaining membership in the lowest MVPA quartile for girls (OR (95%CI) = 3.9 (1.8, 8.2) and boys (OR (95%CI = 2.9 (1.3, 6.4)). 4. Discussion Accelerometer data were analyzed in this study to describe the transition in afterschool sedentary time and physical activity over a 6-yr period. Overall, sedentary time and light intensity activity contributed the most toward after school hours and were also responsible for the most change from baseline to follow-up. In comparison, MVPA represented a relatively low proportion of afterschool time at baseline and continued to decrease with increasing age, which is concerning given the beneficial role of MVPA on cardiometabolic risk factors.22 After adjusting for several covariates, we found a significantly greater decline in afterschool MVPA (min h−1 ) in girls, compared to boys, and among overweight/obese youth, compared to normal weight youth. Moreover, some evidence of tracking was observed, specifically for boys in the most favorable quartile of afterschool sedentary and MVPA time. The transition toward higher sedentary time and lower light activity during afterschool hours is in agreement with previous findings.11 In the older cohort (10–12 yrs at baseline) from the Arundell study, the percentage of the afterschool period (15:30–18:00) as sedentary increased from 38% at baseline to nearly 50% after 3- and 5-yrs of follow-up, whereas the proportion of light intensity activity decreased from 50% to nearly 40% at both follow-up periods. Despite differences in mean age at baseline and length of the afterschool period, similar changes were found in our study for sedentary (37–61% of after school time) and light intensity activity (54–34% of after school time). Although accelerometers provide objective estimates of activity they are unable to identify specific behaviors, therefore we were unable to document changes in specific types of sedentary and light intensity activity. In an earlier study of pre-adolescent youth,10 the 2-yr increase in total sedentary time during the afterschool period was primarily attributed to an increase in non-screen behavior (homework) in boys, whereas among girls the increase in total sedentary
Please cite this article in press as: Wickel EE, Belton S. School’s out . . . now what? Objective estimates of afterschool sedentary time and physical activity from childhood to adolescence. J Sci Med Sport (2015), http://dx.doi.org/10.1016/j.jsams.2015.09.001
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Table 2 6-yr change in afterschool sedentary and MVPA time (min h−1 ) by sex, body size, and ethnic categories. B coefficients (95% CI) Sedentary Unadjusted Sex Baseline BMI Ethnicity Sex × baseline BMI Boys <85th percentile Boys ≥85th percentile Girls <85th percentile Girls ≥85th percentile * ** *** a b c
MVPA b
Adjusted
Unadjusted
Adjustedb −0.94 (−1.47, −0.40)*** −0.65 (−1.22, −0.08)* −0.54 (−1.20, 0.12)
0.28 (−1.19, 1.75) −0.49 (−2.09, 1.10) 2.96 (1.15, 4.76)***
0.28 (−1.00, 1.57) 0.30 (−1.11, 1.70) 2.37 (0.73, 4.02)**
0.18 (−0.53, 0.89) 0.13 (−0.64, 0.90) −0.43 (−1.31, 0.44)
0.65 (−1.70, 2.99) 0.94 (−1.75, 3.62) 1.41 (−0.88, 3.69) –
−0.29 (−2.36, 1.79) 1.11 (−1.23, 3.44) 0.66 (−1.33, 2.64) –
−0.31 (−1.43, 0.81) −0.14 (−1.42, 1.15) −0.11 (−1.21, 0.99) –
1.56 (0.71, 2.41)c 0.73 (−0.21, 1.67) 0.52 (−0.28, 1.31) –
p ≤ 0.05. p ≤ 0.01. p ≤ 0.001. Adjusted for baseline afterschool sedentary time (min h−1 ), change in non-afterschool sedentary time (min h−1 ), difference in afterschool wear time (min), and SES. Adjusted for baseline afterschool MVPA (min h−1 ), change in non-afterschool MVPA (min h−1 ), difference in afterschool wear time (min), and SES. Statistically different to remaining categories (p ≤ 0.001).
time was from increased screen (TV, computer) and non-screen behavior (homework). Interventions to reduce sedentary time have focused on screen-based behaviors.23 Additional research is needed to identify correlates of non-screen sedentary behaviors to provide additional targets for interventions seeking to reduce sedentary behavior. Diminishing levels of MVPA with increasing age have been reported across whole days13 and segments within a day24 ; therefore, the decline we observed in afterschool MVPA was anticipated and also coincides with conclusions from longitudinal11 and crosssectional9 investigations of afterschool hours. In our study, the contribution of afterschool MVPA to daily MVPA remained relatively consistent from childhood to adolescence, suggesting the age-related decline in MVPA during afterschool hours is comparable to the decline during other portions of the day. In contrast to this finding, a previous study11 reported an increase in the contribution of afterschool MPA and VPA to total daily levels with age. The disparity between studies was most likely due to large differences in ‘afterschool’ length (2.5 vs 7 h) and the effect this difference would have on reporting percent contributions from daily segments. Our result was more comparable to the findings from Long et al. (2013) using cross-sectional accelerometer data from the National Health and Nutrition Examination Survey (NHANES). In their study, similar contributions from afterschool (15:00–17:59), evening (18:00–23:59), and combined segments (15:00–23:59) to total daily MVPA were observed between young (mean age ∼9 yrs) and old (mean age ∼ 15 yrs) participants. The observation that afterschool MVPA (operationally defined as 15:00–22:00) contributes a similar percentage of total MVPA during childhood and adolescence (∼50%) is interesting and implies that interventions, occurring during or after school, are both logical targets to increase total daily activity levels. Several interventions have been successful at increasing MVPA during school hours25 ; however, many schools lack resources necessary to facilitate curricular change thereby necessitating the need for additional activity away from school to reach recommended levels of daily activity. Preliminary research26 has demonstrated some success at increasing activity through compulsory healthrelated homework but, to date, results in this area are limited and require further investigation. Although afterschool programs may be a viable option to offset the decline in activity, the availability of these programs is limited27 and, in many cases, much of the time is spent in sedentary and light intensity activity.28 While community organizations may play a role in promoting afterschool activity by developing shared-use partnerships with schools to use indoor/outdoor facilities,29 additional research is needed to
understand the type of play (structured vs unstructured) and style of motivation that will encourage active behaviors. Our study has strengths and limitations. The use of accelerometry and the extended follow-up period (6 yrs) were both major strengths. Although debate exists regarding accelerometer thresholds to quantify sedentary time and physical activity, the thresholds reported by Evenson and colleagues20 have been shown to exhibit high classification accuracy (compared to indirect calorimetry) across a range of intensities21 and were therefore considered appropriate for the current investigation. Using different accelerometers at baseline (Actigraph 7164) and follow-up (Actigraph GT1 M) was a limitation; however, high inter-unit classification agreement has been reported across varying intensities.16 Given the intermittent nature of youth activity,30 the 60-s epoch may have underestimated the actual time in moderate and/or vigorous activity and possibly underestimated the observed decline in afterschool MVPA from childhood to adolescence. Our sample was primarily Caucasian and from upper income families; therefore, the findings may not generalize to specific ethnic minorities or to those of lower SES. Previous studies have operationally defined the afterschool period between 15:30 and 18:00. In girls and boys, nearly 25% of daily activity is accumulated after 18:009 ; therefore, the duration selected for this study was purposeful to comprehensively describe the transition in sedentary time and physical activity during the hours after school from childhood to adolescence. 5. Conclusion Findings from this study add to a limited body of knowledge regarding the change in afterschool activity over time. Overall, the results demonstrate a reduction in afterschool MVPA and an increase in sedentary time with increasing age. Based on our findings, relatively greater concern may exist in girls, especially those who are overweight or obese during childhood. Given the age-related decline in afterschool activity, programs are needed throughout this period that promote the maintenance of activity or encourage additional activity with age. The current study specifically examined the unstructured environment, but it is likely that structured environments that facilitate activity, such as afterschool programs and community involvement, may be beneficial. Practical implications • From childhood to adolescence, afterschool activity decreases and sedentary time increases.
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• The 6-yr decline in afterschool MVPA was greater in girls and overweight/obese children, compared to boys and normal weight children, respectively. • Boys within the most desirable quartile for afterschool sedentary time and MVPA at 9 yrs were, respectively, 4× and 3× more likely to maintain this quartile position at 15 yrs compared to boys in the remaining quartiles. Acknowledgements This study was conducted by the National Institute of Child Health and Development (NICHD) Early Child Care Research Network supported by NICHD through a cooperative agreement that calls for scientific collaboration between the grantees and the NICHD staff. No financial assistance was provided to the authors for the completion of this study. References 1. Janssen I, LeBlanc AG. Systematic review of the health benefits of physical activity and fitness in school-aged children and youth. Int J Behav Nutr Phys Act 2010; 7(1):40. 2. Strong WB, Malina RM, Blimkie CJ et al. Evidence based physical activity for school-age youth. J Pediatr 2005; 146(6):732–737. 3. Ridgers ND, Stratton G, Fairclough SJ. Assessing physical activity during recess using accelerometry. Prev Med 2005; 41(1):102–107. 4. Nettlefold L, McKay HA, Warburton DE et al. The challenge of low physical activity during the school day: at recess, lunch and in physical education. Br J Sports Med 2011; 45(10):813–819. 5. Pate PP, Davis MG, Robinson TN et al. Promoting physical activity in children and youth: a leadership role for schools: a scientific statement from the American Heart Association Council on Nutrition, Physical Activity, and Metabolism (Physical Activity Committee) in collaboration with the Councils on Cardiovascular Disease in the Young and Cardiovascular Nursing. Circulation 2006; 114(11):1214–1224. 6. Biddle SJ, Gorely T, Marshall SJ et al. The prevalence of sedentary behavior and physical activity in leisure time: a study of Scottish adolescents using ecological momentary assessment. Prev Med 2009; 48(2):151–155. 7. Wickel E. Variables associated with active and inactive behavior during the afterschool period. Pediatr Exerc Sci 2013; 25(2):288–299. 8. Atkin AJ, Gorely T, Biddle SJ et al. Critical hours: physical activity and sedentary behavior of adolescents after school. Pediatr Exerc Sci 2008; 20(4):446–456. 9. Long MW, Sobol AM, Cradock AL et al. School-day and overall physical activity among youth. Am J Prev Med 2013; 45(2):150–157. 10. Wickel EE, Issartel J, Belton S. Longitudinal change in active and sedentary behavior during the after-school hour. J Phys Act Health 2013; 10(3):416–422.
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11. Arundell L, Ridgers ND, Veitch J et al. 5-Year changes in afterschool physical activity and sedentary behavior. Am J Prev Med 2013; 44(6):605–611. 12. Sallis JF, Prochaska JJ, Taylor WC. A review of correlates of physical activity of children and adolescents. Med Sci Sports Exerc 2000; 32(5):963–975. 13. Nader PR, Bradley RH, Houts RM et al. Moderate-to-vigorous physical activity from ages 9 to 15 years. JAMA 2008; 300(3):295–305. 14. Barlow SE. Expert committee recommendations regarding the prevention, assessment, and treatment of child and adolescent overweight and obesity: summary report. Pediatrics 2007; 120(Suppl. 4):S164–S192. 15. United States Census Bureau. Poverty thresholds 2000. Available at: www.census. gov/hhes/www/poverty/data/threshld/thresh00.html. Accessed 24 February 2015. 16. Kozey SL, Staudenmayer JW, Troiano RP et al. Comparison of the ActiGraph 7164 and the ActiGraph GT1M during self-paced locomotion. Med Sci Sports Exerc 2010; 42(5):971–976. 17. Dayyat EA, Spruyt K, Molfese DL et al. Sleep estimates in children: parental versus actigraphic assessments. Nat Sci Sleep 2011; 3:115–123. 18. Colley R, Connor Gorber S, Tremblay MS. Quality control and data reduction procedures for accelerometry-derived measures of physical activity. Health Rep 2010; 21(1):63–69. 19. Troiano RP, Berrigan D, Dodd KW et al. Physical activity in the United States measured by accelerometer. Med Sci Sports Exerc 2008; 40(1):181–188. 20. Evenson KR, Catellier DJ, Gill K et al. Calibration of two objective measures of physical activity for children. J Sports Sci 2008; 26(14):1557–1565. 21. Trost SG, Loprinzi PD, Moore R et al. Comparison of accelerometer cut points for predicting activity intensity in youth. Med Sci Sports Exerc 2011; 43(7):1360–1368. 22. Ekelund U, Luan J, Sherar LB et al. Moderate to vigorous physical activity and sedentary time and cardiometabolic risk factors in children and adolescents. JAMA 2012; 307(7):704–712. 23. Salmon J, Ball K, Hume C et al. Outcomes of a group-randomized trial to prevent excess weight gain, reduce screen behaviours and promote physical activity in 10-year-old children: Switch-Play. Int J Obes (Lond) 2008; 32(4):601–612. 24. Ridgers ND, Timperio A, Crawford D et al. Five-year changes in school recess and lunchtime and the contribution to children’s daily physical activity. Br J Sports Med 2012; 46(10):741–746. 25. Howe CA, Freedson PS, Alhassan S et al. A recess intervention to promote moderate-to-vigorous physical activity. Pediatr Obes 2012; 7(1):82–88. 26. Duncan S, McPhee JC, Schluter PJ et al. Efficacy of a compulsory homework programme for increasing physical activity and healthy eating in children: the healthy homework pilot study. Int J Behav Nutr Phys Act 2011; 8(127). 27. Afterschool Alliance. America after 3PM. Available at: www.afterschoolalliance. Accessed 25 org/documents/AA3PM-2014/AA3PM National Report.pdf. February 2015. 28. Trost SG, Rosenkranz RR, Dzewaltowski D. Physical activity levels among children attending after-school programs. Med Sci Sports Exerc 2008; 40(4):622–629. 29. Kanters MA, Bocarro JN, Filardo M et al. Shared use of school facilities with community organizations and afterschool physical activity program participation: a cost-benefit assessment. J Sch Health 2014; 84(5):302–309. 30. Bailey RC, Olson J, Pepper SL et al. The level and tempo of children’s physical activities: an observational study. Med Sci Sports Exerc 1995; 27(7):1033–1041.
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Original research
School’s out . . . now what? Objective estimates of afterschool sedentary time and physical activity from childhood to adolescence Eric E. Wickel a,∗ , Sarahjane Belton b a b
University of Tulsa, College of Health Sciences, USA Dublin City University, School of Health and Human Performance, Ireland
a r t i c l e
i n f o
Article history: Received 27 March 2015 Received in revised form 27 August 2015 Accepted 17 September 2015 Available online xxx Keywords: Accelerometer Moderate-to-vigorous physical activity Sedentary time Youth
a b s t r a c t Objectives: To describe the change in afterschool levels of sedentary time and physical activity from childhood to adolescence. Design: Longitudinal. Methods: 375 youth (50% boys) from the Study of Early Child Care and Youth Development (United States) provided accelerometer data at 9 (2000/01) and 15 yrs (2006/07). Average time spent in sedentary, light, moderate, vigorous, and moderate-to-vigorous physical activity (MVPA; min h−1 ) was reported across the afterschool period (15:00–22:00) and separately across whole days. Mean comparisons were conducted to report between- and within-group differences in afterschool data. Analysis of covariance was used to determine the effect of sex, ethnicity, and baseline body mass index (BMI) on the 6-yr change in afterschool sedentary time and MVPA before and after adjusting for covariates (baseline afterschool sedentary/MVPA time, change in non-afterschool sedentary/MVPA time, difference in afterschool wear time, and socioeconomic status). Results: From 9 to 15 yrs, sedentary time increased and activity decreased during the afterschool period. After covariate adjustment, the decline in afterschool MVPA was significantly greater among girls, compared to boys (B coefficient (95%CI) = −0.94 (−1.47, −0.40)), and among overweight/obese youth, compared to youth with normal BMI values (B coefficient (95%CI) = −0.65 (−1.22, −0.08)). Conclusions: During the transition from childhood to adolescence, afterschool activity (min h−1 ) decreases while sedentary time increases. Programs are needed throughout this period that promote the maintenance of activity or encourage additional activity with age. © 2015 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
1. Introduction Daily physical activity is associated with several health benefits.1 As such, it is recommended that youth accumulate at least 60 min of moderate-to-vigorous physical activity (MVPA) each day.2 On weekdays, active opportunities exist within the school environment in the form of recess, physical education, and active classrooms. Although few youth appear to meet specific MVPA recommendations for recess3 or physical education,4 many accumulate 30 min of MVPA while at school,4 which is the recommended amount.5 In order to reach the daily MVPA guideline, participating in activity outside the timetabled school day is necessary for the majority of youth. In contrast to the structured school environment, the hours after school are relatively more discretionary. During this time,
∗ Corresponding author. E-mail address: [email protected] (E.E. Wickel).
youth participate in a range of active and sedentary behaviors,6 many of which are related to demographic, interpersonal, and environmental factors.7 Many studies examining afterschool hours utilize cross-sectional designs8 where the intent is to characterize time allocation and identify potential targets for intervention. As a result, though it has been shown that the afterschool period is an important contributor to overall MVPA in youth,9 relatively little is known about the transition in afterschool activity from childhood to adolescence. Among the few available studies, one10 reported a decrease in moderate-to-vigorous behaviors from 9 to 11 yrs, while another11 reported a decrease in moderate and vigorous activity among young (5–6 yrs at baseline) and old (10–12 yrs at baseline) cohorts over 3 and 5 yrs. Although both studies reveal a decline in afterschool activity with increasing age, the influence of sex, body size, and ethnicity (which are important biological correlates of daily activity12 ) on this transition is relatively unknown. Understanding the influence of these biological factors during the transition between childhood and adolescence is important for the design of targeted interventions aimed at modifying levels of
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sedentary time and physical activity. Accordingly, the primary aim of this study was to describe the impact of biological factors (sex, body size, and ethnicity) on afterschool levels of sedentary time and physical activity from childhood to adolescence. Moreover, as a secondary aim, this study describes the tracking of afterschool sedentary time and physical activity. Given that few longitudinal studies exist to describe the transition in afterschool time allocation, this study addresses a key gap in the literature.
2. Methods Data for this analysis came from the Study of Early Child Care and Youth Development (SECCYD), a multi-phased prospective study of 1,364 families spanning from birth to 15 yrs. The primarily goal of the SECCYD was to examine the influence of early child care experiences on social, emotional, and physical outcomes during childhood and into adolescence. Details regarding the recruitment and consent process have been thoroughly described13 and are also available from the study’s website (http://www. nichd.nih.gov/research/supported/seccyd/pages/overview.aspx). The SECCYD research protocol was approved by each participating university’s ethics committee (University of Arkansas; University of California; University of Kansas; University of New Hampshire/Wellesley; Pennsylvania State University/University of Pittsburgh; Temple University; University of Virginia; University of Washington; Western Carolina Center; and University of Wisconsin) and written informed consent was obtained from all participating families at the onset of the study. As the study continued, verbal or implied assent was obtained from the participating child. SECCYD data were collected using subjective and objective assessment tools during four phases (Phase I: birth to 3 yrs (1991–1994); Phase II: 54 months through 1st grade (1995–1999); Phase III: 2nd through 6th grade (2000–2004); and Phase IV: 7th through 9th grade (2005–2007)). To specifically explore the transition in afterschool sedentary time and physical activity from childhood to adolescence, we examined data from Phases I (1991), III (2000/01), and IV (2006/07). Sex and ethnicity were recorded at birth. Chronological age (yrs) was determined based on the observation date (Phases III/IV) and the birth date of the participating child. Height and weight collected during Phases III/IV were used to calculate the body mass index (BMI = kg/m2 ) and BMI z-scores. Sex- and age-specific BMI percentiles14 were used to categorize youth as normal (<85th percentile) or overweight/obese (≥85th percentile). The income:needs ratio was viewed as an index of socioeconomic status (SES) and was determined from parent-reported income (including governmental assistance) and corresponding poverty thresholds defined by the United States Census Bureau.15 Physical activity was measured across a 7-day period with the Actigraph 7164 in Phase III (mean age: 9 yrs) and the Actigraph GT1 M in Phase IV (mean age: 15 yrs) (ActiGraph, Fort Walton Beach, FL, USA) using a 60-s epoch. High inter-unit classification agreement (96%) exists across varying intensities16 ; therefore the impact of using different monitors to assess sedentary time and physical activity was likely minimal in the current study. Baseline accelerometer data were primarily collected from March to May (70%), while follow-up data were primarily collected from either March to May (41%) or August to November (30%). Weekday accelerometer data from both phases were processed using ActiLife 6.4.5 from 07:00 to 22:00 (whole day) and separately from 15:00 to 22:00 (afterschool). Although it’s possible that some youth accumulated additional activity after 22:00, the amount is likely low given that typical bed times for youth17 approximate this hour. Implausible data were operationally defined as activity counts·min−1 ≥ 20,00018 and were replaced with zero. Non-wear
time was identified as periods of 60 consecutive zero counts with an allowance of two interruptions during this 60-min period.19 Wear time was reported across the whole day and during afterschool hours by removing total daily and afterschool non-wear time, respectively. Youth providing valid whole day and afterschool data on ≥3 weekdays at 9 and 15 yrs were included in the analysis. Weekdays were considered valid if whole day accelerometer wear time ≥10 h day−1 and afterschool wear time ≥4 h day−1 . Accelerometer data were processed using activity count min−1 thresholds for sedentary (≤100), light (>100 and <2296), moderate (≥2296 and <4012), vigorous (≥4012), and MVPA (≥2296).20,21 Summary statistics (min h−1 and min day−1 ) were calculated at 9 and 15 yrs for the whole day and during afterschool hours. These values were used to report the percent contribution of each category to whole day and afterschool levels. Descriptive statistics were computed for the entire sample, and separately for girls and boys. Group differences were examined using t (independent and dependent) and chi-square tests, while analysis of covariance (ANCOVA) was used to determine the effect of sex, ethnicity (Caucasian, non-Caucasian), and baseline BMI (normal, overweight/obese) on the change in afterschool sedentary and MVPA time (min h−1 ) from childhood to adolescence. Covariates considered for inclusion were baseline afterschool sedentary and MVPA (min h−1 ), change in non-afterschool sedentary and MVPA (min h−1 ), change in accelerometer wear time (min day−1 ), and SES. Models were conducted before and after covariate adjustment and were performed separately for sedentary and MVPA. Nearly 40% of the total sample provided baseline and follow-up accelerometer data within the same season. No significant mean difference was observed in the change in afterschool sedentary time or MVPA between those with data from the same season or those with data from different seasons, therefore the effect of season was not included in the model. Additional analyses using sex-specific quartiles of afterschool MVPA and sedentary time (min h−1 ) were conducted to report the percentage of youth remaining ≤25th (lowest) and > 75th (highest) quartiles at 9 and 15 yrs. The highest quartile reflects greater accumulated levels of sedentary and MVPA; therefore, stability within this quartile would be desirable for MVPA but not for sedentary time. Odds ratios (OR (95% CI)), obtained via binary regression, were calculated to report the likelihood of maintaining membership within a specified quartile and were viewed as an index of tracking. Odds ratios were adjusted for ethnicity, baseline BMI z-score, baseline SES, and the difference in accelerometer wear time (min day−1 ). SPSS 20 was used for data analyses and significance was set at p ≤ 0.05.
3. Results Of the 947 youth who provided at least a single valid day of accelerometer data, a total of 375 (50% boys; 80% Caucasian) met the inclusion criteria at 9 and 15 yrs and were included in the current study. Chi-square analyses did not reveal a difference between excluded and included participants due to sex (2 (1) = 0.27, p = 0.61) or ethnicity (2 (1) = 0.53, p = 0.47); however, excluded participants had higher baseline SES values compared to included participants (4.5 vs 3.8; p = 0.003). Typical wear time during the afterschool period approximated 6 h (86% of the defined afterschool period). Baseline and follow-up descriptive and afterschool data are shown in Table 1, arranged by sex. Sedentary time and light intensity activity contributed the highest proportion of afterschool time at baseline and follow-up, approximating ≥90%. In general, the contribution from MVPA was higher among boys, compared to girls, at both time periods, but significantly declined with increasing age in both groups. Much of the transition in afterschool time allocation over the 6-yr period was attributable to changes
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Table 1 Descriptive and afterschool accelerometer data from baseline to follow-up. Girls (n = 190)
Boys (n = 185) Baseline
Follow-up
Mean change (95% CI)
9.1 (0.3) 18.6 (3.8) 0.64 (1.0) 4.0 (3.4)
15.1 (0.2) 22.8 (4.9) 0.56 (1.0) 5.3 (7.2)
6.0 (6.0, 6.1)b 4.3 (3.8, 4.7)b −0.08 (−0.19, 0.03) 1.3 (0.4, 2.1)b
Contributing percentage of afterschool time. Values are % (SD) Sedentary 37.2 (9.2) 61.3 (10.4) 24.2 (22.6, 25.8)b Light 55.0 (7.3)a 35.4 (9.2) −19.6 (−21.0, −18.3)b Moderate 5.4 (2.5)a 2.3 (2.3)a −3.1 (−3.6, −2.7)b Vigorous 2.4 (2.0)a 1.0 (1.5)a −1.4 (−1.7, −1.1)b MVPA 7.8 (4.2)a 3.3 (3.4)a −4.5 (−5.2, −3.8)b
37.4 (9.4) 52.5 (7.6) 6.7 (3.1) 3.4 (2.7) 10.1 (5.2)
60.8 (11.6) 33.9 (9.0) 3.4 (2.7) 1.9 (2.7) 5.3 (4.7)
23.4 (21.5, 25.2)b −18.6 (−20.1, −17.1)b −3.3 (−3.8, −2.7)b −1.5 (−2.0, −1.0)b −4.8 (−5.7, −3.9)b
Standardized afterschool time. Values are min h−1 (SD) 22.3 (5.5) 36.8 (6.3) Sedentary Light 33.0 (4.4)a 21.2 (5.5) Moderate 3.3 (1.5)a 1.4 (1.4)a a Vigorous 1.4 (1.2) 0.6 (0.9)a MVPA 4.7 (2.5)a 2.0 (2.0)a
22.5 (5.6) 31.5 (4.5) 4.0 (1.9) 2.0 (1.6) 6.0 (3.1)
36.5 (7.0) 20.3 (5.4) 2.1 (1.6) 1.1 (1.6) 3.2 (2.8)
14.0 (12.9, 15.1)b −11.2 (−12.0, −10.3)b −2.0 (−2.3, −1.6)b −0.9 (−1.2, −0.6)b −2.9 (−3.4, −2.3)b
Age BMI BMI z-score SES
a b
Baseline
Follow-up
Mean change (95% CI)
9.0 (0.3) 18.2 (3.2) 0.51 (0.9) 3.8 (2.7)
15.1 (0.1) 23.2 (4.6) 0.61 (0.8) 4.5 (3.6)
6.1 (6.0, 6.1)b 5.0 (4.6, 5.4)b 0.10 (0.01, 0.19)b 0.75 (0.40, 1.10)b
14.5 (13.5, 15.5)b −11.8 (−12.6, −11.0)b −1.9 (−2.1, −1.6)b −0.8 (−1.0, −0.7)b −2.7 (−3.1, −2.3)b
Significant gender difference (p ≤ 0.05). Significant difference between baseline and follow-up (p ≤ 0.05).
in sedentary time and light intensity activity (Table 1). A relatively lower amount of change was observed in afterschool MVPA from 9 to 15 yrs. At baseline and follow-up, daily wear time approximated 13 h and, in general, the contribution of afterschool MVPA to daily MVPA remained relatively consistent in girls (55% at 9 yrs; 48% at 15 yrs) and boys (51% at 9 yrs; 53% at 15 yrs). Unstandardized (B) coefficients (95% CI) describing the change in afterschool sedentary and MVPA time (min h−1 ) across biological factors (reference category for sex (boys), BMI (normal), and ethnicity (non-Caucasians)) are shown in Table 2. In general, the change in sedentary time was similar between girls and boys and between normal and overweight/obese youth. The unadjusted B coefficient for ethnicity was positive and significant (B = 2.96 (1.15, 4.76)), indicating a greater increase in afterschool sedentary time among Caucasians, compared to non-Caucasians, from 9 to 15 yrs. The B coefficient for ethnicity decreased after including covariates (adjusted B = 2.37 (0.73, 4.02)), but remained significant. In regards to MVPA, significant B coefficients were revealed for sex (adjusted B = −0.94 (−1.47, −0.40); p ≤ 0.001)) and BMI (adjusted B = −0.65 (−1.22, −0.08); p ≤ 0.05) indicating a greater 6-yr reduction in afterschool MVPA among girls (compared to boys) and overweight/obese youth (compared to normal weight youth). Although mean MVPA levels declined with increasing chronological age in girls and boys, the adjusted B coefficients across sex × BMI categories indicate a statistically smaller decline among normal weight boys compared to all remaining categories. This particular finding suggests the difference in MVPA decline over the 6-yr period approximated 11 min (1.56 × afterschool duration (i.e., 7 h) = 10.9 min) between normal weight boys and overweight/obese girls. In comparison to normal weight boys, the decline in MVPA among overweight/obese boys and normal weight girls was greater by 5–6 min. Sex-specific quartiles of afterschool sedentary and MVPA were analyzed to report the percentage of youth remaining in the lowest (≤25th percentile) and highest (≥75th percentile) quartiles at 9 and 15 yrs. In general, percentile values for sedentary time (min h−1 ) were similar between girls and boys, and increased from 9 yrs (girls: 25th (18.8), 75th (25.6); boys: 25th (18.4), 75th (25.9)) to 15 yrs (girls: 25th (32.5), 75th (41.0); boys: 25th (33.1), 75th (40.6)). In contrast, percentile values for MVPA (min h−1 ) were slightly lower among girls, compared to boys, and decreased from 9 yrs (girls: 25th (2.7), 75th (5.9); boys: 25th (3.5), 75th (8.2)) to 15 yrs (girls: 25th (0.7), 75th (2.6); boys: 25th (1.2), 75th (4.5)). Relatively few (≤10%)
girls or boys maintained quartile position (≤25th or >75th) for sedentary or MVPA at 9 and 15 yrs. Overall, the odds of maintaining membership in the lowest quartile for sedentary (OR (95%CI) = 3.9 (1.6, 9.4)) and highest quartile for MVPA (OR (95%CI) = 2.8 (1.2, 6.7)) were significant among boys, but not girls. However, the findings also revealed increased odds of maintaining membership in the lowest MVPA quartile for girls (OR (95%CI) = 3.9 (1.8, 8.2) and boys (OR (95%CI = 2.9 (1.3, 6.4)). 4. Discussion Accelerometer data were analyzed in this study to describe the transition in afterschool sedentary time and physical activity over a 6-yr period. Overall, sedentary time and light intensity activity contributed the most toward after school hours and were also responsible for the most change from baseline to follow-up. In comparison, MVPA represented a relatively low proportion of afterschool time at baseline and continued to decrease with increasing age, which is concerning given the beneficial role of MVPA on cardiometabolic risk factors.22 After adjusting for several covariates, we found a significantly greater decline in afterschool MVPA (min h−1 ) in girls, compared to boys, and among overweight/obese youth, compared to normal weight youth. Moreover, some evidence of tracking was observed, specifically for boys in the most favorable quartile of afterschool sedentary and MVPA time. The transition toward higher sedentary time and lower light activity during afterschool hours is in agreement with previous findings.11 In the older cohort (10–12 yrs at baseline) from the Arundell study, the percentage of the afterschool period (15:30–18:00) as sedentary increased from 38% at baseline to nearly 50% after 3- and 5-yrs of follow-up, whereas the proportion of light intensity activity decreased from 50% to nearly 40% at both follow-up periods. Despite differences in mean age at baseline and length of the afterschool period, similar changes were found in our study for sedentary (37–61% of after school time) and light intensity activity (54–34% of after school time). Although accelerometers provide objective estimates of activity they are unable to identify specific behaviors, therefore we were unable to document changes in specific types of sedentary and light intensity activity. In an earlier study of pre-adolescent youth,10 the 2-yr increase in total sedentary time during the afterschool period was primarily attributed to an increase in non-screen behavior (homework) in boys, whereas among girls the increase in total sedentary
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Table 2 6-yr change in afterschool sedentary and MVPA time (min h−1 ) by sex, body size, and ethnic categories. B coefficients (95% CI) Sedentary Unadjusted Sex Baseline BMI Ethnicity Sex × baseline BMI Boys <85th percentile Boys ≥85th percentile Girls <85th percentile Girls ≥85th percentile * ** *** a b c
MVPA b
Adjusted
Unadjusted
Adjustedb −0.94 (−1.47, −0.40)*** −0.65 (−1.22, −0.08)* −0.54 (−1.20, 0.12)
0.28 (−1.19, 1.75) −0.49 (−2.09, 1.10) 2.96 (1.15, 4.76)***
0.28 (−1.00, 1.57) 0.30 (−1.11, 1.70) 2.37 (0.73, 4.02)**
0.18 (−0.53, 0.89) 0.13 (−0.64, 0.90) −0.43 (−1.31, 0.44)
0.65 (−1.70, 2.99) 0.94 (−1.75, 3.62) 1.41 (−0.88, 3.69) –
−0.29 (−2.36, 1.79) 1.11 (−1.23, 3.44) 0.66 (−1.33, 2.64) –
−0.31 (−1.43, 0.81) −0.14 (−1.42, 1.15) −0.11 (−1.21, 0.99) –
1.56 (0.71, 2.41)c 0.73 (−0.21, 1.67) 0.52 (−0.28, 1.31) –
p ≤ 0.05. p ≤ 0.01. p ≤ 0.001. Adjusted for baseline afterschool sedentary time (min h−1 ), change in non-afterschool sedentary time (min h−1 ), difference in afterschool wear time (min), and SES. Adjusted for baseline afterschool MVPA (min h−1 ), change in non-afterschool MVPA (min h−1 ), difference in afterschool wear time (min), and SES. Statistically different to remaining categories (p ≤ 0.001).
time was from increased screen (TV, computer) and non-screen behavior (homework). Interventions to reduce sedentary time have focused on screen-based behaviors.23 Additional research is needed to identify correlates of non-screen sedentary behaviors to provide additional targets for interventions seeking to reduce sedentary behavior. Diminishing levels of MVPA with increasing age have been reported across whole days13 and segments within a day24 ; therefore, the decline we observed in afterschool MVPA was anticipated and also coincides with conclusions from longitudinal11 and crosssectional9 investigations of afterschool hours. In our study, the contribution of afterschool MVPA to daily MVPA remained relatively consistent from childhood to adolescence, suggesting the age-related decline in MVPA during afterschool hours is comparable to the decline during other portions of the day. In contrast to this finding, a previous study11 reported an increase in the contribution of afterschool MPA and VPA to total daily levels with age. The disparity between studies was most likely due to large differences in ‘afterschool’ length (2.5 vs 7 h) and the effect this difference would have on reporting percent contributions from daily segments. Our result was more comparable to the findings from Long et al. (2013) using cross-sectional accelerometer data from the National Health and Nutrition Examination Survey (NHANES). In their study, similar contributions from afterschool (15:00–17:59), evening (18:00–23:59), and combined segments (15:00–23:59) to total daily MVPA were observed between young (mean age ∼9 yrs) and old (mean age ∼ 15 yrs) participants. The observation that afterschool MVPA (operationally defined as 15:00–22:00) contributes a similar percentage of total MVPA during childhood and adolescence (∼50%) is interesting and implies that interventions, occurring during or after school, are both logical targets to increase total daily activity levels. Several interventions have been successful at increasing MVPA during school hours25 ; however, many schools lack resources necessary to facilitate curricular change thereby necessitating the need for additional activity away from school to reach recommended levels of daily activity. Preliminary research26 has demonstrated some success at increasing activity through compulsory healthrelated homework but, to date, results in this area are limited and require further investigation. Although afterschool programs may be a viable option to offset the decline in activity, the availability of these programs is limited27 and, in many cases, much of the time is spent in sedentary and light intensity activity.28 While community organizations may play a role in promoting afterschool activity by developing shared-use partnerships with schools to use indoor/outdoor facilities,29 additional research is needed to
understand the type of play (structured vs unstructured) and style of motivation that will encourage active behaviors. Our study has strengths and limitations. The use of accelerometry and the extended follow-up period (6 yrs) were both major strengths. Although debate exists regarding accelerometer thresholds to quantify sedentary time and physical activity, the thresholds reported by Evenson and colleagues20 have been shown to exhibit high classification accuracy (compared to indirect calorimetry) across a range of intensities21 and were therefore considered appropriate for the current investigation. Using different accelerometers at baseline (Actigraph 7164) and follow-up (Actigraph GT1 M) was a limitation; however, high inter-unit classification agreement has been reported across varying intensities.16 Given the intermittent nature of youth activity,30 the 60-s epoch may have underestimated the actual time in moderate and/or vigorous activity and possibly underestimated the observed decline in afterschool MVPA from childhood to adolescence. Our sample was primarily Caucasian and from upper income families; therefore, the findings may not generalize to specific ethnic minorities or to those of lower SES. Previous studies have operationally defined the afterschool period between 15:30 and 18:00. In girls and boys, nearly 25% of daily activity is accumulated after 18:009 ; therefore, the duration selected for this study was purposeful to comprehensively describe the transition in sedentary time and physical activity during the hours after school from childhood to adolescence. 5. Conclusion Findings from this study add to a limited body of knowledge regarding the change in afterschool activity over time. Overall, the results demonstrate a reduction in afterschool MVPA and an increase in sedentary time with increasing age. Based on our findings, relatively greater concern may exist in girls, especially those who are overweight or obese during childhood. Given the age-related decline in afterschool activity, programs are needed throughout this period that promote the maintenance of activity or encourage additional activity with age. The current study specifically examined the unstructured environment, but it is likely that structured environments that facilitate activity, such as afterschool programs and community involvement, may be beneficial. Practical implications • From childhood to adolescence, afterschool activity decreases and sedentary time increases.
Please cite this article in press as: Wickel EE, Belton S. School’s out . . . now what? Objective estimates of afterschool sedentary time and physical activity from childhood to adolescence. J Sci Med Sport (2015), http://dx.doi.org/10.1016/j.jsams.2015.09.001
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Please cite this article in press as: Wickel EE, Belton S. School’s out . . . now what? Objective estimates of afterschool sedentary time and physical activity from childhood to adolescence. J Sci Med Sport (2015), http://dx.doi.org/10.1016/j.jsams.2015.09.001