A 24-h activity profile and adiposity among children and adolescents: Does the difference between school and weekend days matter?

BACKGROUND: Twenty-four-hour movement behaviours are gaining attention in the research community. However, no study has addressed how 24-h activity profiles vary between structured and less structured days and whether an unfavourable activity profile is associated with childhood obesity. We aimed to analyse differences between school day and weekend day 24-h activity profiles and their associations with adiposity indicators among children and adolescents. METHODS: Participants were 382 children and 338 adolescents who wore wrist accelerometers for 24 hours a day for seven consecutive days. The 24-h activity profile expressed by the average acceleration (AvAcc) and intensity gradient (IG) were estimated from multi-day raw accelerometer data. Adiposity indicators included body mass index (BMI) z-score, fat mass percentage (FM%), fat mass index (FMI), and visceral adipose tissue (VAT). Multiple linear regression of activity profile metrics and adiposity indicators was performed separately for school and weekend days. RESULTS: Weekend days AvAcc and IG were lower compared to school days in both age groups (p <0.001 for all). Specifically, AvAcc was lower by 9.4% and 11.3% in children and adolescents, respectively. IG on weekend days was lower (more negative) by 3.4% in children and 3.1% in adolescents. Among children, on school days AvAcc and IG were negatively associated with FM%, FMI, and VAT, whilst on weekend days AvAcc was positively associated with BMI z-score, FMI, and VAT (p < 0.05 for all). Among adolescents, negative associations were found between weekend day AvAcc and IG and FM% and FMI (p < 0.05 for all), respectively. CONCLUSIONS: This study confirms the importance of 24-h activity profile as a potentially protective factor against excess adiposity. The variability of movement behaviours during structured and less structured days should be considered when optimizing the 24-h movement behaviours to prevent childhood obesity.

Changes in sedentary behavior patterns during the transition from childhood to adolescence and their association with adiposity: a prospective study based on compositional data analysis.

BACKGROUND: To date, no longitudinal study using a compositional approach has examined sedentary behavior (SB) patterns in relation to adiposity in the pediatric population. Therefore, our aims were to (1) investigate the changes in SB patterns and adiposity from childhood to adolescence, (2) analyze the prospective compositional associations between changes in SB patterns and adiposity, and (3) estimate the changes in adiposity associated with substituting SB with physical activity (PA) of different intensities. METHODS: The study presents a longitudinal design with a 5-year follow-up. A total of 88 participants (61% girls) were included in the analysis. PA and SB were monitored for seven consecutive days using a hip-worn accelerometer. Adiposity markers (fat mass percentage [FM%], fat mass index [FMI], and visceral adiposity tissue [VAT]) were assessed using the multi-frequency bioimpedance analysis. The prospective associations were examined using compositional data analysis. RESULTS: Over the follow-up period, the proportion of time spent in total SB increased by 154.8 min/day (p < 0.001). The increase in total SB was caused mainly by an increase in middle and long sedentary bouts, as these SB periods increased by 79.8 min/day and 62.0 min/day (p < 0.001 for both), respectively. FM%, FMI, and VAT increased by 2.4% points, 1.0 kg/m2, and 31.5 cm2 (p < 0.001 for all), respectively. Relative to the remaining movement behaviors, the increase in time spent in middle sedentary bouts was significantly associated with higher FM% (ßilr1 = 0.27, 95% confidence interval [CI]: 0.02 to 0.53) at follow-up. Lower VAT by 3.3% (95% CI: 0.8 to 5.7), 3.8% (95% CI: 0.03 to 7.4), 3.9% (95% CI: 0.8 to 6.9), and 3.8% (95% CI: 0.7 to 6.9) was associated with substituting 15 min/week spent in total SB and in short, middle, and long sedentary bouts, respectively, with an equivalent amount of time spent in vigorous PA. CONCLUSIONS: This study showed unfavorable changes in SB patterns and adiposity status in the transition from childhood to adolescence. Incorporating high-intensity PA at the expense of SB appears to be an appropriate approach to reduce the risk of excess adiposity in the pediatric population.

Associations of novel 24-h accelerometer-derived metrics with adiposity in children and adolescents.

BACKGROUND: Further research is required to explore the associations between 24-h movement behaviours and health outcomes in the paediatric population. Therefore, this study aimed to examine the associations between novel data-driven 24-h activity metrics and adiposity among children and adolescents. METHODS: The sample included 382 children (8-13 years) and 338 adolescents (14-18 years). The average acceleration (AvAcc) of activity, intensity gradient (IG), and metrics representing the initial acceleration for the most active time periods of the 24-h cycle were calculated from raw acceleration data. Adiposity measures included body mass index z-score, fat mass percentage (FM%), and visceral adipose tissue (VAT). Data analysis was performed using multiple linear regression adjusted for wear time, sex, maternal education level, and maternal overweight and obesity. RESULTS: Children demonstrated higher values in all 24-h activity metrics than did adolescents (p < 0.001 for all). For children, the initial acceleration for the most active 2, 5, 15, and 30 min of the 24-h cycle were negatively associated with FM% (p ≤ 0.043 for all) and VAT (p <0.001 for all), respectively. For adolescents, the IG was negatively associated with FM% (p = 0.002) and VAT (p = 0.007). Moreover, initial acceleration for the most active 2, 5, 15, 30, 60, and 120 min were associated with FM% (p ≤ 0.007 for all) and with VAT (p ≤ 0.023 for all). CONCLUSIONS: The intensity distribution of activity and initial acceleration for the most active 2, 5, 15, 30, 60, and 120 min within the 24-h cycle are beneficial for the prevention of excess adiposity in the paediatric population.

Replacing school and out-of-school sedentary behaviors with physical activity and its associations with adiposity in children and adolescents: a compositional isotemporal substitution analysis.

BACKGROUND: Little is known on how context-specific sedentary behaviors (SB) affect adiposity. This study aimed to investigate compositional associations between context-specific SB and adiposity and estimate the differences in adiposity associated with replacing school and out-of-school SB with physical activity (PA). METHODS: This study included 336 children and adolescents. Time spent in SB and PA was estimated using multi-day 24-hour raw accelerometer data. SB and PA were specified for school and out-of-school times. Fat mass percentage (FM%) and fat mass index (FMI) were used as adiposity indicators. A compositional isotemporal substitution model was used to estimate differences in adiposity associated with one-to-one reallocations of time from context-specific SB to PA. RESULTS: Participants spent approximately two thirds of their school and out-of-school time being sedentary. Relative to the remaining 24-h movement behaviors, significant associations between out-of-school SB and adiposity were found in both boys (ßilr1 = 0.63, 95% confidence interval [CI] = 0.03-1.22 for FM%; ßilr1 = 0.76, 95% CI = 0.03-1.49 for FMI) and girls (ßilr1 = 0.62, 95% CI = 0.25-0.98 for FM%; ßilr1 = 0.80, 95% CI = 0.28-1.32 for FMI). Replacing 30 min/day of out-of-school SB with out-of-school light PA decreased FM% by 10.1% (95% CI = 3.3-17.9) and FMI by 14% (95% CI = 2.7-24) in girls. No significant associations were found for school SB. CONCLUSIONS: A reduction of out-of-school SB in favor of light PA should be advocated as an appropriate target for interventions and strategies to prevent childhood obesity.

Prevalence and correlates of adherence to the combined movement guidelines among Czech children and adolescents.

BACKGROUND: There are limited studies on the prevalence of adherence to the combined guidelines for physical activity (PA), sedentary behavior, and sleep in children and adolescents. Moreover, little is known about correlates of adherence to the guidelines. Therefore, the main aim of this study is to examine the prevalence and identify the correlates of adherence to the combined movement guidelines among children and adolescents. METHODS: A total of 355 children aged 8-13 years (44% boys) and 324 adolescents aged 14-18 years (43% boys) from the Czech Republic participated in this study. PA and sleep duration were estimated using multi-day 24-h raw data from wrist-worn accelerometers. Recreational screen time was parent proxy-reported in children and self-reported in adolescents. Seventeen potential correlates were grouped into three homogenous categories for biological and cognitive, behavioral, and family correlates. The multi-level multivariable logistic regression was applied to identify correlates of adherence to combined movement guidelines and to specific combinations of any of two recommendations. RESULTS: Approximately 6.5% of children and 2.2% of adolescents met all recommendations of the combined movement guidelines. In children, girls (OR = 0.4; 95% CI = 0.1-0.9) and participants with overweight or obese fathers (OR = 0.3; 95% CI = 0.1-0.7) had significantly lower odds of adherence to the combined movement guidelines. Additionally, children had higher odds of meeting specific combinations of two recommendations if they reported regular fruit and vegetable intake, participated in organized PA, or if their fathers had a university degree. Meanwhile, paternal overweight and obesity, and high sleep efficiency were associated with lower odds of meeting specific combinations of recommendations. In adolescents, sex, fruit and vegetable intake, organized PA, and active play were correlates of meeting specific combinations of any two recommendations. CONCLUSIONS: A low proportion of children and adolescents met the combined movement guidelines and several correlates related to family were identified. Family is a key source of influence for healthy movement behaviors during childhood and adolescence.

How do short sleepers use extra waking hours? A compositional analysis of 24-h time-use patterns among children and adolescents.

BACKGROUND: To examine compositional associations between short sleep duration and sedentary behavior (SB), light physical activity (LPA) and moderate-to-vigorous physical activity (MVPA) among children and adolescents. METHODS: Multi-day 24-h data on sleep, SB, LPA and MVPA were collected using accelerometers among 343 children (8-13 years old) and 316 adolescents (14-18 years old). Children and adolescents with sleep duration of < 9 and < 8 h, respectively, were classified as short sleepers. Robust compositional regression analysis was used to examine the associations between short sleep duration and the waking-time composition. RESULTS: Seventy-one percent of children and 75.3% of adolescents were classified as short sleepers. In children, being a short sleeper was associated with higher SB by 95 min/day (p < 0.001) and lower MVPA by 16 min/day (p = 0.002). Specifically, it was associated with a higher amount of time spent in long sedentary bouts (ßilr1 = 0.46, 95% confidence interval [CI] = 0.29 to 0.62) and lower amounts of time spent in sporadic SB (ßilr1 = - 0.17, 95% CI = -0.24 to - 0.10), sporadic LPA (ßilr1 = - 0.09, 95% CI = -0.14 to - 0.04) and sporadic MVPA (ßilr1 = - 0.17, 95% CI = -0.25 to - 0.10, p < 0.001 for all), relative to the remaining behaviours. In adolescents, being a short sleeper was associated with a higher amount of time spent in SB by 67 min/day (p = 0.001) and lower LPA by 2 min/day (p = 0.035). Specifically, it was associated with more time spent in sedentary bouts of 1-9 min (ßilr1 = 0.08, 95% CI = 0.02 to 0.14, p = 0.007) and 10-29 min (ßilr1 = 0.10, 95% CI = 0.02 to 0.18, p = 0.015), relative to the remaining behaviours. CONCLUSIONS: Among children and adolescents, short sleep duration seems to be highly prevalent and associated with less healthy waking time. Public health interventions and strategies to tackle the high prevalence of short sleep duration among children and adolescents are warranted.

Is adherence to the 24-hour movement guidelines associated with a reduced risk of adiposity among children and adolescents?

BACKGROUND: Little is known about the combined effect of physical activity (PA), recreational screen time (ST), and sleep in preventing childhood obesity. Hence, this study aimed to analyze the associations between meeting the PA, ST, and sleep recommendations within the 24-hour movement guidelines and adiposity indicators among children and adolescents. METHODS: A total of 679 children and adolescents aged 8-18 years were included. The time spent in moderate-to-vigorous PA and the sleep duration were estimated from raw data from a wrist-worn accelerometer. Recreational ST was reported by the child or parent. Body mass index (BMI) z-score, fat mass percentage (FM%), and visceral adipose tissue (VAT) were used as adiposity indicators. Participants with ≥ 60 min/day of moderate-to-vigorous PA, < 2 h/day of recreational ST, and uninterrupted sleep for 9-11 h/day (for children) or 8-10 h/day (for adolescents) were considered to meet the overall 24-hour movement guidelines. RESULTS: Meeting the ST only recommendation was associated with reduced odds of a high BMI z-score (odds ratio [OR] = 0.38, 95% confidence interval [CI]: 0.17-0.89), excess FM% (OR = 0.34, 95% CI: 0.13-0.93), and excess VAT (OR = 0.27, 95% CI: 0.10-0.74) in adolescents. Significantly reduced odds of a high BMI z-score was associated with meeting the combination of the ST and sleep recommendations (OR = 0.11, 95% CI: 0.01-0.89). Adolescents who met one recommendation (OR = 0.51, 95% CI: 0.27-0.96) or any two recommendations (OR = 0.33, 95% CI: 0.11-0.94) had reduced ORs of having a high BMI z-score. Adolescents had lower odds of having excess VAT if they met one recommendation (OR = 0.39, 95% CI: 0.19-0.81) or any two recommendations (OR = 0.25, 95% CI: 0.07-0.90). No significant associations were found in children. CONCLUSIONS: The present study showed no associations between meeting all three recommendations within the 24-hour movement guidelines and adiposity indicators. However, meeting ST only recommendation and the combination of the ST and sleep recommendations was associated with a reduced risk of excess adiposity. This finding should be considered when designing effective strategies and interventions to prevent childhood obesity.

Physical Activity of Secondary School Adolescents at Risk of Depressive Symptoms.

BACKGROUND: The aim of the study is to analyze the associations between depressive symptoms (DS), well-being and different types of physical activity (PA) in adolescents. METHODS: Overall, 368 girls and 228 boys aged 15-19 years were involved in the research. To explore the composition of weekly PA, we used the IPAQ-Long questionnaire, and a pedometer was used to monitor weekly PA. The prevalence of DS was diagnosed by the Bern Subjective Well-Being Questionnaire and the WHO-5 Well-Being Index. RESULTS: The girls and boys who reported the most DS and the lowest level of well-being had significantly less weekly recreational PA. The girls who reported the fewest DS had a 2.12 times greater odds of meeting the 11,000 steps/day recommendation than did the girls with the most DS, whereas we did not detect statistically significant differences in rates of meeting the recommendation in the boys with distinct levels of DS. CONCLUSIONS: The study confirms the stronger negative associations between DS and PA, especially among girls. The greatest opportunities for behavioral change in adolescents at the highest risk of DS are in the promotion of recreational PA.

Physical Activity in 15-17-Year-Old Adolescents as Compensation for Sedentary Behavior in School.

The traditional concept of education and school settings significantly contribute to the sedentary behavior of adolescents at secondary schools. The aim of this study is to identify the volume and intensity of physical activity (PA) that adolescent boys and girls engage in during recesses, after school, and during the day to compensate for sedentary behavior in lessons. The study was conducted at 29 Czech and 9 Polish schools. The study involved 868 girls and 409 boys aged 15-17 years. An ActiTrainerTM accelerometer was used to monitor PA and heart rate. Participants were divided into four quartile groups. Most sedentary boys and girls had less PA and showed a worse ratio of physical inactivity (PI)/PA than non-sedentary participants during recesses. In the after-school period, there were no significant differences. On school days, most sedentary boys and girls showed lower PA, a worse ratio of PI/PA, fewer steps·hour-1, and lower energy expenditure than their non-sedentary counterparts. Vigorous PA of ≥8 METs was reached by 48% of most sedentary boys (75% non-sedentary) and 47% of most sedentary girls (54% non-sedentary). Most sedentary adolescents do not compensate for their sedentary behavior in lessons with higher PA intensity or volume during recesses, after-school, or in overall daily PA.

Academic Stress and Physical Activity in Adolescents.

The issue of work-related mental health needs to be addressed at the school level. The aim of this study was to explore the associations between academic stress (AS) of adolescent boys and girls and their physical activity (PA) during recesses and after school and to propose measures to promote the adoption of lifelong healthy working habits. Adolescents from 16 schools in the Czech Republic and 6 schools in Poland participated in the study (187 boys and 339 girls). Monitoring of PA and cognitive stress was conducted during one school day. We used ActiTrainer accelerometers to monitor PA and physical inactivity. Data on time of PA and self-reported AS in school lessons were collected using recording sheets. We split the participants into two groups: those without a self-reported stressor and those who indicated one or more stressors. Differences in overall PA during recesses, as well as after-school PA, between boys with and without AS were not statistically significant for any PA characteristics. We observed similar results for girls. Repeated measures ANOVA confirmed that differences in PA (steps/hour) during recesses following particular lessons between participants with and without AS were not statistically significant in boys or girls (F (4,1612) = 1.83, p=0.121 , η p 2=0.005). It is noteworthy that girls with AS were statistically significantly more likely to meet the 6000 steps after school time recommendation (39%) than girls without AS (18%; p < 0.001). The study did not confirm the assumption that adolescents reporting AS have less PA during recesses or even after school than adolescents without AS. However, the overall low PA of adolescents during recesses and after school highlights the need to compensate for AS by adequate PA. This is especially true for adolescents with recurrent AS in several consecutive lessons.

Adolescents' Physical Activity in Education Systems Varying in the Number of Weekly Physical Education Lessons.

Purpose: School physical activity (SPA) is a significant component of daily PA. We investigated differences in PA between boys and girls in two differing education systems-Poland and the Czech Republic-which have four and two physical education lessons (PELs) per week, respectively. Method: This project was conducted from 2012-2016 at 17 Polish and 23 Czech secondary schools (N = 921; mean age = 16.2 ± 0.7 years). ActiTrainer accelerometers were used to monitor participants' PA and heart rate during school days. Weekly PA was measured using pedometers. Subjective levels of weekly PA were self-reported on the International Physical Activity Questionnaire-long form. Results: The Polish education system enabled adolescents to meet the recommendations for moderate-to-vigorous PA more likely than did the Czech system. SPA also represented a higher portion of daily PA in the Polish (vs. Czech system); however, the differences in total daily step count between Polish and Czech adolescents were non-significant. SPA accounted for 30-37% of the daily PA (as measured by step count) of Polish girls (23-30% of Czech girls) and 28-39% of Polish boys (25-37% of Czech boys). Conclusions: Participation in PELs was associated with a higher rate of meeting SPA recommendations in both countries. Compared with the Czech Republic, more PELs in the Polish education system was associated with increased daily vigorous PA and a greater portion of SPA in daily PA. Differences in overall daily and weekly moderate-to-vigorous PA between Polish and Czech adolescents were non-significant.

Validity of Garmin Vívofit 1 and Garmin Vívofit 3 for School-Based Physical Activity Monitoring.

PURPOSE: Activity trackers are useful tools for physical activity promotion in adolescents, but robust validity evaluations have not been done under free-living conditions. This study evaluated the validity of the Garmin Vívofit 1 (G1) and Garmin Vívofit 3 (G3) in different settings and contexts. METHODS: The participants (girls: 52%, age: 15.9 [1.9] y) wore the G1 and G3 on their nondominant wrist and the Yamax pedometer on their right hip for a period of 1 week. Validity was examined in 4 discrete segments (before school, in school, after school, and whole day). The criterion method was the Yamax pedometer. RESULTS: Both the G1 and G3 could be considered equivalent to the Yamax pedometer regarding the before school, in school, and whole day segments. The G1 showed wider limits of agreement than G3. CONCLUSIONS: The G1 and G3 trackers exhibited acceptable validity for 3 of the 4 segments (before school, in school, and whole day measurements). The results were less accurate during the after-school segment. The evidence that the validity of the monitors varied depending on the setting and context is an important consideration for research on adolescent activity patterns.

Associations between accelerometer-measured physical activity and body fatness in school-aged children.

BACKGROUND: The main aim of the study was to examine the cross-sectional associations between objectively measured physical activity (PA) and body fatness in 7-12-year-old children. METHODS: We performed an analysis of 365 children (209 girls). Participant recruitment was performed in eight randomly selected elementary schools in cities and towns with various numbers of inhabitants. The body composition analysis was performed according to a multi-frequency bioelectrical impedance analysis; PA was monitored using an accelerometer. RESULTS: In terms of the overall PA, boys were more active than girls. No significant associations (unadjusted and adjusted models) were found between light PA and all body fatness indicators in either sex. Moderate-to-vigorous PA was significantly negatively associated with all body fatness indicators only in girls. These associations strengthened after adjustment for age, height and sedentary time (ß ranging from -0.49 to -0.36, P ≤ 0.01). In contrast, vigorous PA was strongly negatively associated with body fatness indicators only in boys. In the fully adjusted model the significant negative associations were found for fat mass percentage (ß = -0.15, P = 0.048) and fat mass index (ß = -0.15, P = 0.040). CONCLUSIONS: The present study suggests that increasing sex-specific PA of different intensities may be an appropriate approach for decreasing body fatness in children. Longitudinal studies are needed to verify these associations.

Effect of Accelerometer Cut-Off Points on the Recommended Level of Physical Activity for Obesity Prevention in Children.

There is no general consensus regarding which accelerometer cut-off point (CoP) is most acceptable to estimate the time spent in moderate-to-vigorous physical activity (MVPA) in children and choice of an appropriate CoP primarily remains a subjective decision. Therefore, this study aimed to analyze the influence of CoP selection on the mean MVPA and to define the optimal thresholds of MVPA derived from different accelerometer CoPs to avoid overweight/obesity and adiposity in children aged 7 to 12 years. Three hundred six children participated. Physical activity (PA) was monitored for seven consecutive days using an ActiGraph accelerometer (model GT3X) and the intensity of PA was estimated using the five most frequently published CoPs. Body adiposity was assessed using a multi-frequency bioelectrical impedance analysis. There was found a wide range of mean levels of MVPA that ranged from 27 (Puyau CoP) to 231 min∙d-1 (Freedson 2005 CoP). A receiver operating characteristic curve analysis indicated that the optimal thresholds for counts per minute (cpm) and MVPA derived from the Puyau CoP was the most useful in classifying children according to their body mass index (BMI) and fat mass percentage (FM%). In the total sample, the optimal thresholds of the MVPA derived from the Puyau CoP were 22 and 23 min∙d-1 when the categories based on BMI and FM%, respectively, were used. The children who did not meet these optimal thresholds had a significantly increased risk of being overweight/obese (OR = 2.88, P < 0.01) and risk of having excess fat mass (OR = 2.41, P < 0.01). In conclusion, the decision of selecting among various CoPs significantly influences the optimal levels of MVPA. The Puyau CoP of 3 200 cmp seems to be the most useful for defining the optimal level of PA for pediatric obesity prevention.

Differences in the intensity of physical activity during school days and weekends in Polish and Czech boys and girls.

INTRODUCTION AND OBJECTIVE: The physical, mental and social development that occurs in young people through physical activity (PA) is primarily through extracurricular activities. Family, peers and social environment, in addition to schools, interest groups and school sports, play a unique role during this developmental period. The objective of the study was to examine the differences in the intensity of PA during school days and weekends and the relationship between PA and physical inactivity (PI) during these days in Polish and Czech boys and girls. MATERIALS AND METHODS: In total, there were 816 participants among whom 333 met the requirements of 8 hours of continuous recording of PA (ActiTrainer accelerometers) during at least one school and one weekend day. RESULTS: Boys and girls from both countries engaged in virtually the same amount of PA during school and weekend days, and participated in more PA at lower intensities on the weekends compared with school days. CONCLUSIONS: This study surveyed important issues related to global public health, specifically for the school environment and school settings. The important and crucial relations with family were emphasized, which should increase the awareness and understanding of public health problems of this particular research sample. The results indicated that less time was spent in PI, but also that the largest amount of time during the weekends was spent in front of a screen.

Compensation for Adolescents' School Mental Load by Physical Activity on Weekend Days.

INTRODUCTION AND OBJECTIVE: Increasing mental load and inadequate stress management significantly affect the efficiency, success and safety of the educational/working process in adolescents. The objective of this study is to determine the extent that adolescents compensate for their school mental load by physical activity (PA) on weekend days and, thus, to contribute to the objective measurement of mental load in natural working conditions. METHODS: A cross-sectional study was conducted between September 2013 and April 2014. A set of different methods was employed-self-administered questionnaire (IPAQ-long questionnaire), objective measurements-pedometers, and accelerometers (ActiTrainers). They was distributed to 548 students from 17 high schools. Participants' mental load was assessed based on the difference between PA intensity and/or physical inactivity and heart rate range. RESULTS: The participants with the highest mental load during school lessons do not compensate for this load by PA on weekend days. CONCLUSIONS: Adolescents need to be encouraged to be aware of their subjective mental load and to intentionally compensate for this load by PA on weekend days. It is necessary to support the process of adopting habits by sufficient physical literacy of students, as well as teachers, and by changes in the school program.

The Role of Physical Education Lessons and Recesses in School Lifestyle of Adolescents.

BACKGROUND: This study investigates school lifestyle among adolescents in terms of physical activity (PA) structure: (1) adolescents participating in a physical education lesson (PEL) versus (2) aggregate recess time exceeding 60 minutes. METHODS: The research was conducted in 24 secondary schools in the Czech Republic (boys N = 208, girls N = 433). For the whole day (1-3 days) participants wore the ActiTrainer accelerometer, which monitored PA, and heart rate. A total of 1122 school days were recorded. RESULTS: Both boys and girls participating in a PEL reported significantly better results compared with nonparticipating individuals regarding all indicators of volume and intensity of school PA (SPA). In most SPA indicators, longer aggregate recess time (>60 minutes) had a statistically significant effect, particularly on the volume of SPA. The recommended 500 steps/hours for SPA was achieved by 83% of boys participating in PEL and 69% of girls. In contrast just 32% of nonparticipating boys and 31% of girls reached this level. With longer recess time the recommendation was met by 43% of boys (42% of girls) compared with 26% of boys (23% of girls) with shorter recess time. CONCLUSIONS: An increase in SPA and an improved lifestyle in adolescents on school days are significantly supported more by PELs than by longer recess time.

Mental Load and Its Compensation by Physical Activity in Adolescents at Secondary Schools.

AIM: Sedentary behaviour and increasing mental load in adolescents is one of the major health problems of the contemporary youth. The aim of the study is to analyze the associations between mental load and physical activity (PA) in adolescents in school-day segments. METHODS: 381 adolescents (120 boys, 261 girls) took part in the research which was conducted in 19 secondary schools in the Czech Republic. Participants throughout the whole day (1-3 days) wore an ActiTrainer accelerometer that monitors PA and heart rate (HR). The reports covered 727 school days. The participants were divided into two groups with lower and higher mental load. RESULTS: Boys and girls with higher mental load in lessons do not compensate this load in neither volume nor intensity of PA during recess in greater amount than those who had lower mental load. In the individual school-day segments (apart from the time before school) no significant differences between the groups were found. CONCLUSION: When creating a habit of immediate compensation for mental load in lessons by PA, it is necessary to pay attention to boys and girls with higher mental load in lessons. The adoption of the habit should be supported by adequate physical literacy of both students and teachers and by changes in the school programme.