Why have youth physical activity trends flatlined in the last decade? Opinion piece on “Global trends in insufficient physical activity among adolescents: a pooled analysis of 298 population-based surveys with 1.6 million participants” by Guthold et al.

1.No global progress on youth physical activity prevalenceTagedEnd TagedPDespite hundreds of intervention studies over decennia that have been dedicated to developing and testing programs and strategies to promote physical activity(PA)in adolescents,14 global inactivity levels remain persistently high.Based on self-report data from 1.6 million schoolgoing adolescents from 146 countries,Guthold et al.5 confirmed previous urgent calls to get adolescents more active.Researchers from the World Health Organization(WHO)recently published global prevalence rates and the first ever global time trends for insufficient PA in youth.They reported that more than 80%of school-going adolescents globally did not meet the current recommendations of at least 1 h of PA per day.

Does light-intensity physical activity moderate the relationship between sitting time and adiposity markers in adolescents?

Background:While the relationship between sedentary time and adiposity markers may be independent of moderate-to-vigorous intensity physical activity(MVPA) among adolescents,little is known about the role of light-intensity physical activity(LIPA) in this relationship.The aim of this cross-sectional study was to examine whether device-measured LIPA and MVPA moderate the associations between objectively measured sitting time and adiposity markers(body mass index(BMI)) and waist circumference(WC)) among adolescents.Methods:This study included accelerometer and inclinometer data obtained from 219 adolescents(age=14.9±1.6 years,mean± SD),collected during 2014 and 2015 in Melbourne,Australia.ActiGraph GT3 X accelerometers were used to determine time spent in total-LIPA(101 counts/min to 3.99 metabolic equivalents(METs)) was dichotomized into low-LIPA(101-799 counts/min) and high LIPA(800 counts/min to 3.99 METs),and MVPA(> 4 METs).The average time spent sitting was obtained from activPAL inclinometers.Anthropometric measures were assessed by trained staff.Interactions between sitting and total-LIPA,low-LIPA,high-LIPA,and MVPA on BMI z-score(zBMI) and WC z-score(zWC),respectively,were examined using linear regression,adjusting for age and sex;and moderation by total-LIPA,low-LIPA,high-LIPA,and MVPA were examined by adding interaction terms.Significant interaction effects were probed by comparing associations at the mean and at 1 SD below and above the mean.Results:Total-LIPA significantly moderated the association between sitting time and zBMI,and low-LIPA significantly moderated the association between sitting time and zBMI and zWC.No other associations were found for total-LIPA,high-LIPA,or MVPA.Specifically,at high levels of total-LIPA(+1 SD),there is a negative association between sitting time and zBMI.In addition,at high levels of low-LIPA(+1 SD),there is a negative association between sitting time and zBMI and zWC.Conclusion:Associations between sitting and adiposity depended on time spent in total-LIPA and low-LIPA,but not high-LIPA or MVPA.Results suggest that increasing time spent in LIP A may provide protection from the deleterious effects of sitting on adiposity markers among adolescents.Experimental evidence is needed to support these conclusions.

Activity-related typologies and longitudinal change in physical activity and sedentary time in children and adolescents:The UP&DOWN Study

Background:Children and adolescents can be distinguished by different typologies(clusters) of physical activity and sedentary behavior.How physical activity and sedentary behaviors change over time within different typologies is not known.This study examined longitudinal changes in physical activity and sedentary time among children and adolescents with different baseline typologies of activity-related behavior.Methods:In this longitudinal study(3 annual time points) of children(n=600,age=9.2±0.4 years(mean±SD),50.3% girls) and adolescents(n=1037,age=13.6±1.7 years,48.4% girls),participants were recruited in Spain in 2011-2012.Latent class analyses identified typologies based on self-reported screen,educational,social and relaxing sedentary behaviors,active travel,muscle strengthening activity,and sport at baseline.Within each typology,linear mixed growth models explored longitudinal changes in accelerometer-derived moderate-to-vigorous physical activity and sedentary time,as well as time by class interactions.Results:Three typologies were identified among children( "social screenies",12.8%;"exercisers",61.5%;and "non-sporty active commuters",25.7%) and among adolescents "active screenies",43.5%;"active academics",35.0%;and "non-sporty active commuters",21.5%) at baseline.Sedentary time increased within each typology among children and adolescents,with no significant differences between typologies.No changes in physical activity were found in any typology among children.In adolescents,physical activity declined within all typologies,with "non-sporty active commuters" declining significantly more than "active screenies" over 3 years.Conclusion:These results support the need for interveation to promote physical activity and prevent increases in sedentary time during childhood and adolescence.Adolescents characterized as "non-sporty active commuters" may require specific interventions to maintain their physical activity over time.

Feasibility of breaking up sitting time in mainstream and special schools with a cognitively challenging motor task

Background: Children spend 70% of the school day sitting in class. Classroom-based active breaks can benefit children's physical health, but if the breaks are cognitively demanding(i.e., combine physical exertion and mental engagement), they may also improve focus and cognitive functions. Teachers and students play a crucial role in the successful implementation of active breaks, and their perspectives are critical to the feasibility of these strategies. The aim of this study was to assess the feasibility of implementing a cognitively challenging motor task as an active break in mainstream and special primary schools.Methods: A total of 5 teachers in 2 mainstream schools and 7 teachers in 1 special school(attended by children with neurodevelopmental disorders) attended a 20-min training on how to implement a 4-min cognitively challenging active break, before conducting a feasibility trial(twice a day for 1 week). To understand individual perceptions, one-on-one semistructured interviews were conducted before and after the trial with teachers, and focus group interviews were conducted with typically developing children after the trial. Questions were based on a predefined framework for feasibility studies. All interviews were audio recorded, transcribed and analyzed in NVivo 11 using a framework approach. A total of 12 teachers(11 females; 7 between 20 and 34 years old) and 34 children(16 girls; 9.3 § 1.7 years, mean § SD) participated in the interviews.Results: In mainstream schools, teachers viewed the cognitively challenging motor task as appropriate and potentially beneficial for children's health and focus. Children reported enjoying the active breaks. Teachers in special schools viewed the task as complex and potentially frustrating for children. In both school types, children's disruptive behavior and lack of time were seen as the main potential barriers to implementation. The use of music, videos, visual cards, and support staff were noted as potential facilitators.Conclusion: The cognitively challenging motor task was a feasible way to interrupt children's sitting time and promote physical activity in mainstream schools, but required changes in special schools. Further research could investigate the effectiveness of these types of task interruptions on children's physical and cognitive health.

The impact of height-adjustable desks and classroom prompts on classroom sitting time,social,and motivational factors among adolescents

Purpose:This quasi-experimental study examined the impact of height-adjustable desks in combination with prompts to break up prolonged sitting time during class time and identified social and motivational factors associated with breaking up sitting time among adolescents.Teachers’perceptions of strategies were also examined.Methods:Over 17 weeks,1 classroom in a government secondary school in Melbourne,Australia,was equipped with 27 height-adjustable desks and prompts(posters and desk stickers)to break up classroom sitting time.Teachers received professional development in the use of the desks and prompts.One group of adolescents(n=55)had 2-5 lessons/week using the height-adjustable desks in an intervention classroom,and a comparison group matched by year level and subject(n=50)was taught in traditional“seated”classrooms.Adolescents wore an activPAL monitor at baseline(T0),4 weeks(T1),and 17 weeks(T2)and completed a survey at T0 and T2.Six teachers participated in interviews at T2.Effect sizes were calculated(d).Results:Linear mixed models found that,compared to the traditional“seated”classrooms,the adolescents in the intervention classroom had significantly lower sitting time(T1:-9.7 min/lesson,d=-0.96;T2:-6.7 min/lesson,d=-0.70)and time spent in sitting bouts>15 min(T2:-11.2 min/lesson,d=-0.62),and had significantly higher standing time(T1:7.3 min/lesson,d=0.84;T2:5.8 min/lesson,d=0.91),number of breaks from sitting(T1:1.3 breaks/lesson,d=0.49;T2:1.8 breaks/lesson,d=0.67),and stepping time(T1:2.5 min/lesson,d=0.66).Intervention classroom adolescents reported greater habit strength(d=0.58),self-efficacy for breaking up sitting time(d=0.75),and indicated that having a teacher/classmate remind them to stand as helpful(d=0.50).Conclusion:This intervention shows promise for targeting sitting behaviors in the classroom and indicates that incorporating social and motivational strategies may further enhance outcomes.

Using compositional data analysis to explore accumulation of sedentary behavior,physical activity and youth health

Purpose:The study aimed to describe youth time-use compositions,focusing on time spent in shorter and longer bouts of sedentary behavior and physical activity(PA),and to examine associations of these time-use compositions with cardiometabolic biomarkers.Methods:Accelerometer and cardiometabolic biomarker data from 2 Australian studies involving youths 7-13 years old were pooled(complete cases with accelerometry and adiposity marker data,n=782).A 9-component time-use composition was formed using compositional data analysis:time in shorter and longer bouts of sedentary behavior;time in shorter and longer bouts of light-,moderate-,or vigorous-intensity PA;and"other time"(i.e.,non-wear/sleep).Shorter and longer bouts of sedentary time were defined as<5 min and>5 min,respectively.Shorter bouts of light-,moderate-,and vigorous-intensity PA were defined as<1 min;longer bouts were defined as≥1 min.Regression models examined associations between overall time-use composition and cardiometabolic biomarkers.Then,associations were derived between ratios of longer activity patterns relative to shorter activity patterns,and of each intensity level relative to the other intensity levels and"other time",and cardiometabolic biomarkers.Results:Confounder-adjusted models showed that the overall time-use composition was associated with adiposity,blood pressure,lipids,and the summary score.Specifically,more time in longer bouts of light-intensity PA relative to shorter bouts of light-intensity PA was significantly associated with greater body mass index z-score(zBMI)(β=1.79;SE=0.68)and waist circumference(β=18.35,SE=4.78).When each activity intensity was considered relative to all higher intensities and"other time",more time in light-and vigorous-intensity PA,and less time in sedentary behavior and moderate-intensity PA,were associated with lower waist circumference.Conclusion:Accumulating PA,particularly light-intensity PA,in frequent short bursts may be more beneficial for limiting adiposity compared to accumulating the same amount of PA at these intensities in longer bouts.