Purpose To describe physical activity (PA) intensity across a school day and assess the percentage of girls and boys achieving recommended guidelines.
Methods The authors measured PA via accelerometry in 380 children (8–11 years) and examined data representing (1) the whole school day, (2) regular class time, (3) recess, (4) lunch and (5) scheduled physical education (PE). Activity was categorised as sedentary (SED), light physical activity (LPA) or moderate to vigorous physical activity (MVPA) using age-specific thresholds. They examined sex differences across PA intensities during each time period and compliance with recommended guidelines.
Results Girls accumulated less MVPA and more SED than boys throughout the school day (MVPA −10.6 min; SED +13.9 min) recess (MVPA −1.6 min; SED +1.7 min) and lunch (MVPA −3.1 min; SED +2.9 min). Girls accumulated less MVPA (−6.2 min), less LPA (−2.5 min) and more SED (+9.4 min) than boys during regular class time. Fewer girls than boys achieved PA guidelines during school (90.9% vs 96.2%), recess (15.7% vs 34.1%) and lunch (16.7% vs 37.4%). During PE, only 1.8% of girls and 2.9% of boys achieved the PA guidelines. Girls and boys accumulated similar amounts of MVPA, LPA and SED.
Conclusion The MVPA deficit in girls was due to their sedentary behaviour as opposed to LPA. Physical activity strategies that target girls are essential to overcome this deficit. Only a very small percentage of children met physical activity guidelines during PE. There is a great need for additional training and emphasis on PA during PE. In addition schools should complement PE with PA models that increase PA opportunities across the school day.
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Compelling evidence supports a beneficial relationship between moderate to vigorous physical activity (MVPA) and a variety of chronic disease risk factors in school-aged children.1 Physical activity (PA) in children decreases adiposity in those who are overweight, decreases blood pressure in those with hypertension1 and enhances skeletal2 and cardiovascular3 health. Over the last several decades, increasing numbers of children around the world have been classified as overweight or obese.4 Although the root of obesity is complex, evidence suggests that low PA and increased sedentary (SED) behaviour may be partially responsible.5 6
The school environment is an attractive option for delivering health-promoting PA. Children spend approximately 30 h/week in school, and boys and girls from a range of socioeconomic backgrounds and ethnicities that might be difficult to access otherwise are included.7 8 However, schools may not be living up to their potential. Although physical education (PE) and recess are likely opportunities for school PA, evidence suggests that curricular time devoted to PE is declining.9 Furthermore, MVPA during PE is lower10,–,13 than recommended,14 although MVPA differs by sex.10 15 Recess MVPA is also lower than recommended,16 17 although this finding is not consistent.18
Beyond the well-known benefits of MVPA for cardiovascular,1 3 skeletal1 2 and mental health1 and the focus on MVPA in school-based studies,10 15,–,17 19 light physical activity (LPA) may also provide benefits by contributing to daily energy expenditure.20 In addition, SED is an independent risk factor for all-cause and cardiovascular mortality in adults.21 22 Very few studies have described the spectrum of PA intensity from SED to MVPA during the school day. Moreover, those investigations included only boys,13 did not distinguish between SED and LPA,23 or examined only recess,13 23 lunch23 and/or PE.13
A number of studies demonstrated that habitual MVPA was lower in girls compared with same-age boys.24 However, few studies investigated when during the school day these differences occurred and whether there was also a sex difference in SED and LPA. Therefore, the primary objectives of this cross-sectional study were to (1) describe the amount of SED, LPA and MVPA undertaken by elementary school girls and boys throughout a typical school day (whole school day, classroom time, recess, lunch and scheduled PE) and (2) compare whether activity intensity differed between girls and boys during each time interval. The secondary objectives of this study were to (1) describe girls' and boys' compliance with recommended guidelines for MVPA throughout a typical school day and (2) compare whether guideline compliance differed between girls and boys during each time interval. The guidelines applied for school-day PA were (1) 30 min of MVPA accumulated during the whole school day (Canada: BC Ministry of Education27), (2) 40% of the recess and lunch breaks in MVPA (UK16) and (3) 50% of PE in MVPA (USA14). We hypothesised that (1) girls would accumulate more SED and less PA (LPA and MVPA) compared with boys and (2) a smaller proportion of girls compared to boys would meet PA guidelines.
Participants were a subset of 629 children (aged 8–11 years) attending nine elementary schools in the Vancouver area (table 1) that were participating in a larger cluster randomised controlled trial evaluating the effectiveness of a school-based PA model (Action Schools! BC (AS!BC)). Briefly, AS!BC helps elementary schools create customised action plans to increase PA opportunities for children in the school environment (described in detail elsewhere26). Written informed consent was obtained from parents/guardians and children gave verbal and written assent. This investigation was approved by the human research ethics boards at the Universities of British Columbia and Victoria.
Descriptive characteristics include age, height, body mass and body mass index (BMI). Height (without shoes) was measured twice to the nearest millimetre using a portable stadiometer (model 214; Seca, Hanover, Maryland, USA). Body mass was measured twice to the nearest 0.1 kg using an electronic scale (model 840, Seca). If height or body mass measures differed by more than 0.4 cm or 0.2 kg, respectively, a third measure was taken. The average of the two closest values or the median of three equidistant values was used. Decimal age was calculated using date of measurement and birth and BMI was calculated as body mass divided by height squared (kg/m2).
PA data were collected between November 2005 and February 2006, before the implementation of AS!BC (ie, baseline data). PA was measured using GT1M ActiGraph monitors (ActiGraph, Pensacola, Florida, USA). The GT1M is a small (3.8×3.7×1.8 cm) solid-state accelerometer that detects vertical acceleration signals in the range of 0.05–2.00g. The signal is band limited to the frequency range of 0.25–2.50 Hz. Accelerometer counts are summed over a user-specified epoch (interval), which we set at 15 s for the purposes of this investigation.
Research assistants distributed accelerometers to participants at school and provided instruction on correct wear. Accelerometers were attached to an elastic belt and worn at the hip. Participants were asked to wear the accelerometer during waking hours for five consecutive days and to remove only for sleeping, bathing and swimming. Participants were given a log sheet to record accelerometer on and off times each day. With the exception of one school (where distribution was Friday morning and collection Tuesday afternoon), all accelerometers were distributed on a Wednesday and collected the following Monday morning. PA monitoring and physical measurements (height, weight) were 2.5 weeks apart, on average.
Data reduction and analysis
Accelerometer files were screened for spurious data points (extremely high values) and patterns (extended periods of the same count value). Participants were included if they had at least 10 h of data on three or more days. At the one Friday to Tuesday school, we constructed a full school day using half of Friday (12:45 to school end) and Tuesday (school start to 12:45). The mean and 95% confidence interval (CI) of motionless bout length (ie, extended periods of zeros)25 was 25 ± min. Therefore, periods of continuous zeros ≥30 min were considered biologically implausible and excluded from our analysis. For our analysis, only activity during the regular school day (approximately 9:00 to 15:00) is reported. The primary variables of interest were (1) MVPA (≥3 metabolic equivalents (METs)), (2) LPA (1.5–2.9 METs) and (3) SED (<1.5 METs).
We used age-specific cut points to classify PA intensity.24 We applied cut points for SED, LPA and MVPA that were developed and validated in a group of 80 children aged 6–17 years.24 The calibration study was laboratory based and used regression analysis to determine the relationship between exercise intensity (by respiratory gas exchange measures) and accelerometer counts. We then used custom software (Kinesoft version 2.0.94, Kinesoft Software, New Brunswick, Canada) to extract minutes of PA during (1) the whole school day, (2) regular class time (excludes recess, lunch and scheduled PE), (3) recess, (4) lunch and (5) scheduled PE. Data for a time period were discarded if participants were missing data during that time period (ie, motionless bouts longer than 30 min). Therefore, the sample size for time periods varied (fig 1). To account for variations in the length of time periods, we expressed time spent in PA at each level of intensity as (1) minutes accumulated and (2) a proportion of the total time.
To ascertain whether PE had taken place as scheduled, we cross-checked PE schedules with weekly teacher activity logs. If a teacher reported PE as per the schedule, PE was deemed “verified”. If a teacher's log did not match the PE schedule, or if activity logs were not completed, PE was deemed “unverified”. Only verified PE classes were included in the analyses.
Statistical analyses were performed using STATA V.10.1 (StataCorp, College Station, Texas, USA). We used independent t tests to compare descriptive characteristics between included and excluded participants and one-way analysis of variance weighted by the number of days of data per child to compare the intensity of girls' and boys' PA during each time period. We used recommended guidelines to determine the proportion of participants who (1) accumulated 30 min of MVPA during the school-day,27 (2) spent 40% of the recess and lunch breaks in MVPA16 and (3) spent 50% of PE in MVPA14 and χ2 tests to evaluate associations between sex and guideline achievement. Results were considered significant at p<0.05.
Sample sizes and reasons for participant exclusion are provided in fig 1. Of the 629 children who were recruited, 68 were not measured (moved residence between consent and measurement, absent, incomplete consent) (fig 1). Of the 561 measured participants, we excluded those who had malfunctioning accelerometers, insufficient data or an invalid school day (ie, school holiday). On four dates there were insufficient accelerometers for all children; and although pedometers were provided, their data were excluded (fig 1). Final sample sizes were 380 for lunch, 379 for whole school day, classroom and recess, and 216 for PE. There were 272 participants (150 girls, 122 boys) with two valid school days and 108 participants (48 girls, 60 boys) with one valid school day. There were 46 participants (22 girls, 24 boys) with two verified PE classes and 170 participants (91 girls, 79 boys) with one verified PE class.
Several participants were not measured for height (n=7) or body mass (n=6). Age, height and body mass were similar between the 198 included girls and the 91 excluded girls (table 1). Age and BMI were similar between the 182 included boys and the 90 excluded boys. However, included boys were shorter (−2.3 cm, 95% CI −4.2 to −0.5 cm) and weighed less (−3.2 kg, 95% CI −5.8 to −0.6 kg) (data not shown) than excluded boys.
Whole school-day activity
The school day ranged in length from 345 to 387 min. Girls accumulated less MVPA and more SED compared to boys (table 2). Accumulated LPA was similar between girls and boys (table 2). Overall, the compliance with school-day PA guidelines of 30 min/day was high (>90%). Approximately 5% fewer girls than boys met the recommended target (figure 2).
Regular class time excluded recess, lunch and PE (if applicable) and ranged in length from 240 to 322 min. Girls accumulated less MVPA, less LPA and more SED compared to boys (table 3).
Recess ranged in length from 15 to 25 min. Girls accumulated less MVPA and more SED compared to boys (table 4). The amount and percentage of LPA accumulated was similar between girls and boys (table 4). Only 15.7% of girls and 34.1% of boys achieved guidelines for PA during recess (figure 2).
Lunch ranged in length from 35 to 50 min. Girls accumulated less MVPA and more SED compared to boys (table 5). The amount and percentage of LPA accumulated was similar between girls and boys (table 5). Only 16.7% of girls and 37.4% of boys met the guidelines for PA during lunch (figure 2).
Scheduled PE class activity
Scheduled PE ranged in length from 30 to 45 min per class. The amount and percentage of MVPA, LPA and SED accumulated was similar between girls and boys (table 6). Girls spent 13% and boys 11.4%, of their time in MVPA during PE (table 6). Very few children (<5%) met the guidelines for PA during PE (figure 2).
We extend the existing literature by reporting SED and LPA in addition to MVPA across the entire elementary school day. Our most startling finding was that less than 5% of children met the recommendation for physical activity during school PE. Our hypotheses of lower PA levels and low compliance to PA guidelines in girls compared with boys held true, with the exception of scheduled PE where compliance to recommended guidelines was similarly low for girls and boys. Similar to previous studies,28,–,30 girls accumulated fewer minutes of MVPA than boys across the school day, on average. Two novel findings were that (1) girls appeared to replace MVPA with sedentary behaviour and were more sedentary than boys and (2) girls and boys engaged in similar amounts of LPA except in the classroom where boys were more active. Although both girls and boys struggled to meet recommended physical activity guidelines at recess, lunch and PE girls were less likely than boys to meet current guidelines during the school day, at recess and at lunch.
Whole school day and classroom activity
Our data for MVPA are similar to three previous studies that assessed school-day PA in girls and boys. Mota et al30 measured MVPA in children aged 8–15 years across an assumed 9:00 to 14:59 school day. The total amount of MVPA reported (46 min for girls and 63 min for boys) is similar to the amount we report (53 minutes for girls and 63 minutes for boys). Gidlow et al31 reported accelerometer counts/min across the school day in children aged 3–16 years. Although they did not compare girls and boys statistically, average counts per minute were 382 for girls and 493 for boys. Our data also support an investigation in sixth-grade students where boys accumulated nearly 2000 more steps during the school day than girls.32 Importantly, our finding that although girls and boys engaged in similar amounts of LPA, girls were more SED than boys. Thus, girls are replacing MVPA with sedentary activities rather than participating in a greater proportion of lighter-intensity PA.
Interestingly, classroom PA behaviours also differed between the sexes. Previous investigations did not isolate classroom PA; however, we observed that girls were also less active (MVPA and LPA) and more SED compared to boys during classroom lessons. This speaks to the need for targeted classroom-based PA models that engage both sexes.
Current guidelines suggest that children should engage in at least 30 min of MVPA during the school day.7 8 27 Most of the children (>90%) in our study achieved this goal. However, 5% fewer girls compared to boys were achieving the recommended amount of MVPA.
Recess and lunch activity
The percentage of time this cohort spent in MVPA during recess (20% to 28%) and lunch (30% to 35%) is similar to a previous study of 5- to 10-year-old children from the UK.16 However, other studies have reported MVPA engagement of 63% to 78% in third- to fifth-grade children18 and 50% in 6- to 12-year-old boys.13 Most previous studies16 18 33,–,35 but not all17 reported less MVPA in girls compared to boys. To our knowledge, only one previous study reported LPA and SED in addition to MVPA during recess.13 Boys (6–12 years) in that study accumulated substantially less SED and engaged in more LPA compared with boys in our study.13
The differences between studies may be partially explained by (1) how PA was measured, (2) the study sample, (3) school policies and (4) climate and geography. First, whereas we used accelerometers to quantify MVPA, Beighle et al18 used pedometers (Walk4Life) with an activity time function. This device groups PA intensities together, whereas we report different intensity levels separately. Wickel and Eisenmann13 defined non-wear as 20 min of consecutive zeros in comparison to our definition of 30 min and used different thresholds to classify PA intensity. This may yield different estimates of SED time36 and PA levels.37
Second, we recruited children from schools, whereas Wickel and Eisenmann13 recruited boys from local youth sport programmes. A positive relationship between MVPA during sport practice and unstructured PA (ie, total PA excluding youth sport, recess and PE) suggests that children who are active during sport practice are also active during other aspects of their lives (such as recess and lunch). In addition, our age range (8–11 years) is narrower than previous studies (6–12 years).13 It is well documented that, on average, older children are less active than younger children.24
Third, school policies that define the length or structure of recess and lunch may also explain differences between studies. In our study, recess was 15–25 min long and lunch ranged from 35 to 50 min. We do not know how school policy specifically influenced PA during these periods (ie, whether children had to sit and eat before playing outside). These data were also not provided in previous studies.
Fourth, there were also differences in the geography and climate where studies were conducted. Our study was conducted in Vancouver, Canada, during the winter months (November to February), whereas previous studies were conducted in the southwestern USA during spring (May),18 central USA (month not reported),13 the northwest of England during summer and spring (July and March)16 33 35 and Portugal during spring/summer (May and June).17
We suggest that it is a call to action when only 16% of girls are meeting the recommended proportion of time spent in MVPA during recess and lunch. Current guidelines suggest that 40% of recess and lunch time should be spent in MVPA.16 Approximately 34% of boys met the guidelines during recess and 37% of boys met the guidelines during lunch. This differs from two previous studies from the UK. First, among 5- to 10-year-old children, alarmingly, only 4% of girls and 15% of boys met the guidelines.16 Second, among 6- to 10-year-old children 44% of normal weight boys, 30% of overweight boys, 22% of normal-weight girls and 34% of overweight girls met the guidelines.35
Taken together, these findings highlight the urgent need to provide more and/or facilitated opportunities for PA during school breaks. Environmental variables such as equipment availability, access to suitable play areas and high levels of adult supervision are associated with higher levels of PA;38 therefore, these factors may be useful targets for intervention.
Scheduled PE class activity
Our most startling finding was the almost negligible proportions of time during PE spent in MVPA. These levels (11% to 13%) are substantially lower than previous studies that report 37% to 40% of PE class in MVPA.10 11 13 Our cohort of boys were also more sedentary than 6- to 12-year-old boys in a previous study.13 The PE curriculum in British Columbia prescribes learning outcomes in three areas: (1) active living (includes knowledge and participation), (2) movement skills, and (3) safety, fair play and leadership.39 Therefore, it is possible that the PE classes we assessed focussed more on the non physical activity aspects of the curriculum. Regardless, it seems imperative that the delivery of PE be altered so that children at least achieve guidelines for MVPA.
There were several differences between our study and previous investigations of PE activity. First, in other studies, PE specialists taught all15 32 or most10 PE classes. In our study, all PE classes were taught by the regular classroom teacher (in most cases a generalist). Sports, play and active recreation for kids (SPARK), a school-based PE programme, showed that specialist teachers were more effective at increasing time students spent in MVPA compared with trained generalist teachers (40 vs 33 min weekly40). Thus, it appears that despite focused training for generalist teachers, the need for advanced specialisation in PE may be necessary to effectively enhance children's PA levels during PE. Second, several previous investigations used direct observation (System for observing fitness instruction time (SOFIT))rather than accelerometry to classify PA intensity.10 15 With SOFIT, student-level PA is estimated by coding children's body position (lying, sitting, standing, walking, vigorous)). The “vigorous” category includes any activity that is more intense than walking but does not distinguish beyond that.
Our findings did not support our hypothesis that girls would engage in less MVPA and more light and sedentary activities compared with boys. In previous studies third-grade,10 fourth-grade41 and fifth-grade15 boys were more active in PE than girls, on average. We noted that boys and girls were equally inactive within PE. Our results support two previous studies that reported no sex differences in fifth grade students in accelerometer counts per minute42 nor did step counts during PE class differ between sixth-grade girls and boys.
Guidelines for PA during PE class14 recommend 50% of PE time be spent in MVPA. Disturbingly, in our study, less than 5% of girls and boys met these guidelines (fig 2). Given the structured nature of PE, it is not surprising that boys and girls were similarly inactive during this PE class time. These findings are dire and speak to the urgent need to evaluate both the nature of the PE curriculum and its delivery. They also highlight the need to provide children with other opportunites to engage in physical activity throughout the school day. Indeed, innovative school-based PA models outside of structured PE that compliment but do not replace PE may be one effective solution to offset these negative findings. There are many excellent examples of how such models have been effectively incorporated as part of school culture.43,–,46
Limitations of the present study
We acknowledge several limitations. First, we did not assess physical maturity. Previous research suggests that sex differences in PA levels are eliminated after controlling for maturity.47 As girls mature earlier than boys, they may be less physically active compared with same-age but less mature boys. Second, although we cross-checked school PE schedules with teacher's PA logs and excluded those data that were not supported by teacher logs or where there were discrepancies, teacher data may have been recorded incorrectly. Third, we did not directly observe the activities reported by teachers. Fourth, we applied cut points to estimate minutes of PA from accelerometer data. Previous research suggests different cut points can yield different estimates of PA.37 However, although the number of minutes within PA intensity categories may change with different cut points, the relative differences between boys and girls would likely remain true (ie, more SED and less MVPA in girls compared to boys).
The propensity for sedentary behaviour in girls may have negative health implications. Thus, it seems prudent to provide school-based models that facilitate opportunities for PA and effectively engage girls as a school priority. As very little is known about sex-specific behaviours that explain these gender differences in PA this is an attractive avenue for future study. A better understanding of the social or biological factors that influence sex differences in PA would effectively inform the design and implementation of school-based PA models.
Although most children were meeting the whole school-day PA guidelines further opportunities to engage children more effectively during recess, lunch and during PE are being missed. The extremely high proportion of children (approximately 97%) not meeting the PE MVPA guidelines is especially troubling. This serves as a call to action for school systems that have replaced PE instruction by specialist teachers with generalist teachers to (1) provide additional training or (2) consider alternate or complimentary (to PE) models of PA that provide children with more targeted opportunities to be more physically active during the school day.
What is already known about this topic
Current research suggests that girls engage in less habitual physical activity (PA) compared with same-age boys during childhood.
What this study adds
Our study extends the current literature by examining when during the school day sex differences in PA occur (whole school day, classroom, recess, lunch and physical education) and by reporting that a very small number of children (<5%) are meeting the recommended guidelines for physical activity during PE.
The authors would like to thank the principals, teachers, parents and children in Action Schools! BC schools for their support and participation in the study. The authors would also like to thank Leslie Horita and Dominik Zbogar for assistance with data collection, Josh VanLoon for assistance with the processing of accelerometer data files and Dr Penny Brasher for statistical guidance. DERW is a MSFHR Scholar and a CIHR New Investigator, and LN is a CIHR and MSFHR-funded Doctoral trainee. We are grateful for the support from CIHR (OCO 74248; PJN, PI) and CFI (accelerometers) for this project.
Competing interests None.
Ethics approval This study was conducted with the approval of the University of British Columbia; University of Victoria.
Provenance and peer review Not commissioned; externally peer reviewed.
Detail has been removed from this case description/these case descriptions to ensure anonymity. The editors and reviewers have seen the detailed information available and are satisfied that the information backs up the case the authors are making.
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