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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Keywords:©2006The American College of Sports Medicine
EXERCISE; PHYSICAL EDUCATION; STUDENTS; BEHAVIOR