The prevalence of obesity among the U.S. pediatric population is the highest in the world (41). Body mass and stature directly measured in the National Health and Nutrition Examination Survey (NHANES) shows a threefold increase in overweight (defined as the 95th percentile of age- and sex-specific body mass index derived from five previous NHANES surveys) of 6- to 19-yr-olds, from approximately 5% in 1988-1994 to approximately 16% in 1999-2002 (13,20). Although overweight children may not always become overweight adults, the immediate consequences include cardiovascular risk factors (e.g., hypertension, high cholesterol, glucose intolerance) as well as psychological and social hardships (19).
Without doubt, inappropriate and excess energy intake contributes to the current state of affairs. However, there also is mounting evidence to indicate the detrimental effects of insufficient physical activity (PA) in youth. Although recently an expert panel assembled by the U.S. Centers for Disease Control and Prevention (CDC) recommended at least 60 min of moderate to vigorous PA (MVPA) daily (30), the National Association for Sport and Physical Education (NASPE) guidelines call for at least 60 min and up to several hours of PA daily (18). Only 8% of elementary, 6.4% of junior/middle, and 5.8% of high schools provide daily physical education (PE) for students in all grades (2). Although Scruggs et al. (27) determined (using pedometers to assess stepping rate) that it is feasible for elementary students to be moderately to vigorously active for at least a third of PE class time, 50% is not likely realistic. Unfortunately, based on a study of fifth-grade students, there are concerns that students may achieve MVPA less than 9% of actual class time (29). Further, although there is evidence to suggest that walking short trips (i.e., less than a mile) may have increased in youth between 1995 and 2001 (12), active commuting (i.e., walking or bicycling) behaviors fall far short of public health objectives. A recently published national survey indicated that only 14% of children and adolescents actively commute to and from school (10). Compounding these problems, 25% of American youth watch television four or more hours daily (6).
Because the majority of youth attend school, interventions delivered through this channel are appealing. Detailed and objective understanding of children's typical PA patterns throughout the school day is lacking, however. Simple and inexpensive pedometers can be used to explore these patterns, although it must be acknowledged that pedometers are most sensitive to ambulatory activities and are not able to directly discriminate PA intensity. However, they are readily acceptable to frontline practitioners, and their utility is enhanced with the availability of relevant descriptive data. Therefore, the primary purpose of this study was to describe the patterns of school children's daily pedometer-determined PA (i.e., primarily ambulatory in nature and without direct reference to intensity) during PE, recess and lunchtime, and before and after school. A secondary purpose was to examine sex-specific differences in these patterns.
All sixth-grade students (N = 114 total) representing four classrooms within one elementary school in Mesa, AZ were invited to participate in this study in the spring of 2003. Mesa is an urban community (2003 population = 446,033). The particular elementary school studied has a total population of 748 students (49% girl; 51% boy); 82% are Caucasian, 12% are Hispanic, 3% are African American, 2% are Native American, and 1% are Asian. Additionally, 19% of students were on the free/reduced lunch program, and 34% were bused to school. Students were informed of the study verbally during school hours, sent home with informed consent forms for parent/guardian's written permission, and provided their own written assent to participate. The institutional review board at Arizona State University approved all procedures. A total of 88 students (34 boys and 54 girls) agreed to participate and received parental consent. Based on sex-specific mean and group standard deviation steps per day published previously for 11-yr-olds (36), a sample size of 66 (with a 70:30 unbalanced group size) was minimally required to satisfy two-tailed significance testing at alpha = 0.05 and 80% power (15). Additional students were recruited to buffer against loss attributable to missing data or other noncompliance issues.
Accidental resetting can be a problem when collecting data using unsealed pedometers in children (21). We therefore used a pedometer (Walk4Life LS2500, Plainfield, IL) that had large digital displays (to facilitate self-recording) and a delayed reset button (important to reduce likelihood of accidental resets). The LS2500 is a step-only pedometer; the multifunction equivalent (Walk4Life LS2525) was considered among six pedometers (including the Yamax Digi-walker SW-701) that are accurate (i.e., detecting within ± 1% error at 80 m·min−1) and therefore appropriate for research purposes (4). Recently, Beets et al. (1) demonstrated the acceptable accuracy of a similar Walk4Life pedometer (model LS2505) for detecting steps taken in children compared with the more commonly used Yamax products. All the Walk4Life pedometers are based on the same internal measurement mechanism and only differ on output alternatives. All pedometers used herein were first screened using shake (40) and walking (33) tests.
Although the students at this school had prior experience using pedometers in PE class, study participants were further familiarized with pedometers and protocols 2 d prior to formal data collection. Specifically, participants were instructed on pedometer attachment (at the waist), its removal (only during showering, bathing, swimming, or sleeping), checking their step counts at specific times during the day (details described below), and reattaching and resetting the pedometer each morning upon awakening and dressing. They were also instructed not to tamper with the pedometer and to go about their normal activities during the monitoring frame.
Data collection took place Monday through Wednesday each week for 2 wk. A background questionnaire was used to collect simple demographic information (i.e., age, sex, race/ethnicity). Body mass (to the nearest 0.1 kg) and stature (to the nearest 0.5 cm) were directly measured without shoes. The specific pedometer data collection protocol was adapted from previous work (39). Students wore pedometers beginning in the morning and removed them just prior to bedtime. Unique to this study, research staff were present in the school (i.e., waiting in corridors, libraries or lounges, and outside of student sightlines) throughout data collection to provide instructions as needed and enhance recording compliance by prompting students to note the number of steps accumulated at designated time points during the day (e.g., at commencement of the first class of the school day, at the end of the last class of the school day, at the end and the beginning of the two classes, respectively, abutting recess and lunchtime). Each day, two of the four classrooms monitored participated in a 30-min PE class in the morning before the lunch break; additional prompts were duly conducted specifically at the beginning and end of the PE class (i.e., both measures were taken when students were present in the gymnasium/multipurpose room). A certified PE specialist taught the class, and the curriculum used has been described previously (22). The daily lunch break was 40 min and was held in the gymnasium/multipurpose room; students were typically encouraged by school staff to finish eating in approximately 25 min and to clean up and play for approximately the last 15 min (in the gym or outside). These times are approximate; this schedule was not rigidly enforced, and students were free to play as long as they wished (individual play time was not recorded). The afternoon recess was scheduled for 15 min each day. Students were instructed to record their day-end pedometer steps on their own and to return the data to research staff at the school the next morning. Before accumulating a new day of data, students were asked to reset their pedometer to zero each morning upon awakening. No precise records of time worn were maintained. Data were continuously checked and edited (i.e., data sheets were reviewed, and missing and odd values were queried immediately) during the monitored school days to ensure data completeness and quality. There were no differences in timetables for school days monitored other than scheduling of PE.
Data treatment and statistical analysis.
Descriptive data are presented as means ± SD or frequencies as appropriate. Body mass index (BMI) was computed as kg·m−2. Mean total steps per day were computed as well as steps per day attributed to before-school, recess, lunchtime, and after-school PA. Because PE was only offered on two of the data collection days, steps per day attributable to PE represents the average of only those days. We were able to compute crude steps per minute for PE, recess, and lunchtime because we knew the allotted time for these segments; these time periods were not precisely measured, so stepping rate is presented only descriptively, and no additional inferential statistics were undertaken on these variables. Steps taken throughout the remainder of the school day were considered residual and were computed as total daily steps minus before-school, recess, lunchtime, and after-school PA (PE was only subtracted from those days on which it took place). Independent t-tests and η2 effect sizes (only in the case of statistical significance) were used to examine sex-specific differences (represented as Δ). η2 values of of 0.01, 0.06, and 0.14 were interpreted as small, medium, and large effect sizes, respectively (11). Dependent t-tests were used to examine differences in total steps per day on PE days versus non-PE days, stratified by sex, for those children for whom we had complete data for both types of days. The proportions of boys meeting 13,000 steps per day and girls meeting 11,000 steps per day were evaluated as indicative of meeting the President's Council on Physical Fitness and Sports (PCPFS; www.presidentschallenge.org) PA award thresholds (i.e., daily levels of achievement required for award recognition). Similarly, the proportions of boys meeting 15,000 steps per day and girls meeting 12,000 steps per day were evaluated as indicative of meeting BMI-referenced PA cut points (36).
These analyses are based on 81 students (28 boys and 53 girls) who completed data collection requirements (i.e., provided 4 d of data). Descriptive data for study participants appear in Table 1. There were no statistically significant sex differences in age, BMI (or stature or weight, data not shown), or ethnicity. Pedometer-determined PA was not correlated with either age or BMI and did not differ significantly (assessed by ANOVA) by ethnicity (polychotomous or dichotomous groupings).
Table 2 is a summary of pedometer-determined PA over four school days for this sixth-grade sample. Boys took significantly more total steps per day than girls (η2 = 0.15, large) and more steps during release time (e.g., recess Δ = 479 steps, η2 = 0.15, large; lunchtime Δ = 608 steps, η2 = 0.14, large; and after-school Δ = 1872 steps, η2 = 0.08, medium), with the exception of before-school steps (Δ = 280 steps). Boys and girls took the same number of steps during structured PE classes (P = 0.87). Residuals could only be computed taking into consideration PE class or not, and are presented below. For visual impact, Figure 1 portrays the relative contribution of the segmented day to total pedometer-determined PA in both sexes (representing only the average of the 2 d on which PE was scheduled). Overall, stepping rates for PE, recess, and lunchtime were 47, 78, and 53 steps per minute (48, 99, and 63 steps per minute for boys vs 47, 67, and 48 steps per minute for girls). No other stepping rates could be estimated because precise records of time worn were not maintained.
Table 3 displays the data stratified by PE days versus non-PE days. Boys took significantly more total steps per day on PE days versus non-PE days (P < 0.05), partly because of a combination of more steps during recess and lunchtime as well as during PE class. In contrast, total steps per day did not differ for girls between PE days and non-PE days (P = 0.92). The only segment of the day that differed for girls represented residual steps taken; on non-PE days, girls appeared to be more incidentally active during the school day. Finally, 71.4% of boys and 64.2% of girls achieved the PCPFS sex-specific step-per-day thresholds, and 54.7% of boys and 53.6% of girls met BMI-referenced cut points.
The sixth-grade Arizona children in this study attended an elementary school and appeared to be considerably more active (boys = 16,421 ± 5,444 and girls = 12,332 ± 3,056 steps per day) than a comparable sample of sixth-grade children drawn from two middle schools in California and South Carolina (boys = 10,229 ± 1,598 and girls = 7782 ± 1312 steps per day; geographical breakdown not presented) (24). Although the pedometer used in the latter study differed from that used herein, a separate head-to-head comparison demonstrated that the two instruments are comparably valid for PA assessment in children (1) and therefore cannot explain the differences noted. Besides the geographical and social ecological comparisons, however, it is possible that similarly aged children behave differently based on enrollment in elementary versus middle school. An examination of the determinants of variation in pedometer-determined PA between schools is beyond the scope of this study, however warranted. Regardless, the data herein are consistent with those previously published that represent pedometer-determined PA in children and youth (8,25,39) and once again emphasize that boys accumulate more steps per day than similarly aged girls.
The PCPFS pedometer-based PA award thresholds (i.e., 13,000 and 11,000 steps per day for boys and girls, respectively) were set based on norm-referenced, or expected, values determined from a U.S. sample (39). Based on a large international sample, we recently set preliminary criterion-referenced cut points for steps per day associated with healthy BMI in 6- to 12-yr-old children: 12,000 steps per day for girls and 15,000 steps per day for boys (36). A discussion of the relevance of these cut points and whether there should be different standards based on sex is outside the purview of this article, but these questions have been addressed previously (36). If a stepping rate of approximately 100 steps per minute (representative of the floor of moderate-intensity walking) is strictly applied (37), the BMI-referenced cut points are consistent with Epstein et al. (7), who reviewed 26 studies of heart rate-measured PA in youth and concluded that youth need 120-150 min·d−1 of total PA. The cut points are also consistent with both the CDC-assembled expert panel recommendations (30) and the NAPSE guidelines that suggest children need at least 60 min and up to several hours of PA daily (18). As would be expected, a larger proportion of children herein achieved the lower step-per-day cut points, but the overall difference between the two approaches amounted to a difference of only 16.7% for boys and 10.6% for girls. Of note, just over half of both boys and girls in the present study met the more rigorous BMI-referenced cut points, a testament to the fact that although these cut points are achievable, more American children need to be meeting them.
A key finding was that boys took significantly more steps than girls during release time segments (i.e., recess, lunchtime, after school), with the exception of before-school steps, but boys and girls took the same number of steps during structured PE classes. Further, boys took similar numbers of steps during both recess and PE (despite the former being 15 min shorter), yet girls took 400 fewer steps at recess (release time) compared with PE (structured time). Stated another way, compared with recess, PE contributed relatively more (yet still modestly) to girls' daily PA; both segments contributed equally (and modestly) to boys' daily PA. All of these statements must be interpreted with the caveat that variance in behavior was great within these small segments. For example, because we did not collect precise time in PA, the lunchtime break could be differentially characterized by longer eating and sitting or playing (i.e., a recess break), or vice versa. Aggregated data indicate that boys have a preference for outdoor-play PA (in contrast to quieter play indoors) (23) and have a penchant for more vigorous-intensity activities (32). Further, although the boys and girls herein were of the same age and grade level, Thompson and colleagues (31) have determined that controlling for maturational age negates sex-specific differences in PA behaviors because girls mature earlier than boys. Specifically, because we know pedometer-determined steps per day to generally decrease with maturity (3), we would anticipate that the more developmentally mature girls would be expected to be less physically active than less developmentally mature boys, albeit chronologically equal in age.
As stated above, residual steps were computed as the total daily steps minus those recorded from each of the delineated segments; remaining steps approximate those taken during the course of the school day (e.g., walking and other movement within classes). Residual steps represented approximately 8-16 and 11-13% of total daily PA for girls and boys, respectively, depending on type of day (i.e., PE day or not). Because much of the academic school day is necessarily spent sitting, occasions for PA are typically limited to scheduled breaks (recess, lunchtime) and PE class. This rigorously scheduled sedentarism makes opportunities for after-school PA of utmost importance if an overall healthful level of PA is to be maintained.
After-school PA (representing steps taken between the end of the school day and bedtime) accounted for almost half of this sample's daily total PA, regardless of sex. Unfortunately, a determination of the specific types of activities engaged in after school was beyond the scope of this study. Obviously, a preference for sedentary leisure-time activities including watching television and playing video games would conflict with more physically active behaviors. The wide standard deviations in steps taken observed in this and other segments of the school day suggest that interindividual variation was indeed great and warrants further study.
Steps taken during PE class accounted for 8 and 11% of total steps per day (on days on which children participated in PE) for boys and girls, respectively. Flohr and Todd (8) reported that a small sample (N = 45) of 12- to 14-yr-old schoolchildren took approximately 2000 steps during PE (approximately 600 more steps than recorded herein), yet their overall steps per day on weekdays was lower than our own data (10,576-12,597 vs 13,746 steps per day). The length of the class studied was not reported in that study. Scruggs et al. (28) studied 257 children in first through fourth grades and determined that 1740-1890 steps (more for younger grades) in a 30-min class was representative of minimal standards (i.e., 10 min of MVPA and 33.33% of time in MVPA) for third- and fourth-grade children. The lessons in the current study were designed to balance instruction and skill development in addition to providing a source of PA (22). The third- and fourth-grade children in the Scruggs et al. (28) study took 300-400 more steps than the children in the current study for the same class length, suggesting that the children herein did not meet the suggested minimum lesson time in MVPA. Applying the Scruggs et al. (28) findings, 1400 steps is approximately equal to 27% of class time in MVPA, which is still more than what earlier evidence had indicated-that is, that schoolchildren achieve MVPA less than 9% of actual PE class time (29).
It is obvious that the content of PE classes will vary, likely on a day-to-day basis, and even within a single school. At this time, the accumulated data indicate that a range of 1400-1900 steps is achieved in elementary PE classes that are 30 min in length. This is in line with what has been previously recommended by Morgan et al. (17). In contrast, Reed et al. (24) recently reported that sixth-grade boys averaged 1598 steps, and girls took 1312 steps over two 45-min classes. Adjusting steps by the time of class indicates a range from as low as 29 steps per minute up to 67 steps per minute. Interestingly, the lowest stepping rates are from the longest classes, suggesting that additional PE time does not necessarily translate to additional PA. Of course, it is too early to make firm conclusions about these hypotheses. Further, it is important to emphasize once again that PE classes are guided by multiple educational objectives in addition to providing an opportunity for PA. Regardless, to aid future comparisons, studies should report contextual factors including type of curriculum, whether the class is taught by a specialist or nonspecialist, amount of time the pedometer is attached during PE, allocated time for PE, whether PE is taught inside or outside the school, and climatological factors if applicable. Further, if different class lengths are to be compared (e.g., 30 vs 45 min), then steps per minute appears to be the appropriate metric for evaluation purposes. For these short time frames, this process is as simple as dividing total steps taken by the lesson time. For more complex comparisons, pedometers that possess a timing mechanism or accelerometers might prove useful (1).
We were also able to impute stepping rate estimates for recess (78 steps per minute) and lunchtime (53 steps per minute). Kilanowski (14) reported a stepping rate of 41 steps per minute in 10-yr-old children engaged in an "active recreational period" lasting between 73 and 132 min. Louie and Chan (16) reported 58.8 steps per minute for preschool children playing freely during a 25-min PA class. Taken together with the emerging PE-related evidence, these initial and fragmented data suggest that stepping rates are higher for briefer play (and perhaps unstructured) periods and for younger children (because of age-related height and stride differences). Further, preliminary evidence suggests a difference in stepping rate related to size and location (outdoor vs indoor) of play space (16). As stated above, such comments are largely speculative at this time and require further investigation before they can be generally accepted.
Dale and colleagues (5) studied the impact of restricting PA during the school day (specifically suppressing PE and recess PA) on involuntary after-school PA using a uniaxial accelerometer as the primary assessment tool in third- and fourth-grade children (38 boys and 40 girls). They found no evidence of compensatory PA after school on PA-restricted days, but involuntary lunchtime PA and total daily PA were significantly lower (in addition to the manipulated time periods). We also found no difference in after-school PA on PE and non-PE days in all children. However, boys' PA during lunchtime did appear to be affected by participation in PE. PE (for the classes studied) herein was scheduled immediately before lunchtime. PE participation may have "primed" the boys for more PA; this was not the case for the girls, whose PA (even total daily PA) outside of PE class was not positively impacted by that day's participation. In fact, their residual PA appeared to be reduced on PE days.
Although sex-specific differences were still apparent (i.e., boys > girls), lunchtime PA represented the most important source of daily PA obtained during school hours for both boys and girls. We must emphasize that lunchtime was also a recess break. Although we do not know who rushed through lunch to play and who extended their lunch, the variance in steps taken during lunch is somewhat less than the mean, suggesting that active behavior was an important part of the lunchtime period for most participants. Other studies have determined through systematic observational assessment procedures that levels of engagement in MVPA are typically higher during lunchtime than recess (42) or general free time in the playground (26). Lunchtime PA possibly represents another untapped source of daily PA for school children.
One of the limitations of this study is that pedometers are not designed to directly capture intensity of PA (i.e., without also capturing a more precisely measured time segment); therefore, we cannot make conclusions about children's overall time spent in MVPA over the full day. Trost et al. (32) used an uniaxial accelerometer to describe age- and sex-specific differences in time spent in MVPA by school children in grades 1-12; their results are congruent with the current findings. The accelerometer used in the Trost et al. study possesses a timing mechanism and a memory capacity that records movement parameters over brief units of time (e.g., 1 min); use of this instrument in future studies can provide more precise evaluation of daily time segments. The output, PA counts, are interpreted using cut points that have been developed in laboratory studies (9) and that can therefore be used to estimate PA duration in specific intensity categories. This instrument provides much more information than the simple pedometer used herein, but the requisite technology is expensive. Although prices are decreasing, accelerometers may cost as much as $350-400 per unit and entail additional hardware, software, and technical proficiency to calibrate, input, distill, and analyze data (35). Pedometers provide an acceptable alternative for both researchers and practitioners interested in a more feasible approach to PA assessment in youth. It is anticipated that accelerometer-determined step counts will be higher than those reported herein based on prior research indicating discrepant, although correlated, values detected by concurrently worn accelerometers and pedometers (34). It should also be noted that neither accelerometers nor pedometers are able to detect energy expenditure associated with isometric contractions (i.e., "freezes" or held positions popular in PE classes), other resistance training and flexibility movements, or many nonambulatory movements (e.g., arm movements).
Another limitation of this study is that the findings are based on a relatively small and self-selected sample of children from a single grade at a single elementary school. Therefore, the conclusions may not be generalizeable to other children in other schools. Further, it remains possible that the presence of research staff in the school during the monitoring frame may have elicited reactivity. It is also possible that the mere act of self-recording data may have produced inflated values, although there is no evidence to indicate such reactivity in children using either sealed (38) or unsealed (21) pedometers. As stated above, these data are consistent with other studies that have also used pedometers to describe PA in youth (8,25,36,39). Regardless, the protocol established herein for collecting pedometer data during the segmented school day provides a template to be replicated in larger and more representative samples.
In summary, the uniqueness of this present study lies in the analysis of the pedometer-determined PA during the segmented school day (i.e., before school, during PE, recess, lunchtime, and after school), performed to better understand patterns of PA throughout the day. The findings add to the cumulative evidence (based on a variety of measurement approaches) that boys are more active than similarly aged girls. After-school PA represents approximately half of children's daily total PA, regardless of the child's sex. Lunchtime PA represented the most important source of daily PA (15-16%) obtained during school hours for both boys and girls, whereas recess accounted for 8-9% and PE class accounted for 8-11% of total steps per day. Both lunchtime and recess represent opportunities for daily PA compared with PE, which was only offered twice a week at this particular school. This study provides detailed and objective descriptions of children's typical PA patterns throughout the school day and can be used as comparative data for researchers and practitioners involved in assessment and interventions in youth.
This project was funded in 2003-2004 by a competitive seed grant awarded by the Research Consortium American Alliance for Health, Physical Education, Recreation, and Dance (AAHPERD).
Dr. Pangrazi is a consultant for Walk4Life. No other coauthor has a professional relationship with companies or manufacturers who will benefit from the results of this study. The results of the present study do not constitute endorsement of any product by the authors or ACSM.
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