The prevalence of overweight children and adolescents has more than doubled since the 1960s4
while at the same time their participation in physical activity has declined dramatically, especially among girls,1
indicating the need to improve the understanding of children’s physical activity patterns.
An area of particular concern has been the dramatic decline in children’s active commuting.24
Research has found that children who walk to school engage in more physical activity than those who travel by car, yet the numbers of children who walk to school has been in steady decline.11
These findings underscore the importance of the Healthy People 2010
objective to increase the number of active trips to school made by children who live within a mile of school.2
This study found that middle school girls who reported walking for transportation before and after school on at least one day of a 3-day self-report had significantly higher levels of total physical activity and MVPA before school, before and after school, and for an entire day than did girls who reported none. The highest total physical activity as shown in is seen with girls who report travel by walking before and after school combined, followed by before school walking and then by after school walking. The number of girls reporting after school walking for transportation was 18% and the number of girls reporting before school walking was 14%. These data include girls from six different states and mostly suburban settings (San Diego, Tucson, New Orleans, Baltimore, and Minneapolis). South Carolina schools were located in relatively small cities and towns. Thus, our objective evidence of increased activity in girls who travel by walking before and after school as measured by accelerometry is confirmed by the contextual evidence from the modified 3DPAR that travel by walking is the most frequently reported activity, as shown in . The two different measures of activity provide supporting information.
The only national data on school travel comes from the Nationwide Personal Transportation Surveys (NPRS), now called the National Household Travel Survey (NHTS).25
Walking as a percent of school trips among US children between the ages of 5 and 15 y declined from ~ 20% in 1977 to less than 15% in 2001. Girls in the current study had before school walking rates similar to what was observed in the NHTS study (14%). Lower rates of walking were reported in studies involving two rural states.26,27
In West Virginia, 7.6% of students walked to school and the average time spent walking to school was 7.6 min (SD=4.4), as estimated by principals from elementary, middle, and high schools.26
A similar number (7.5%) of middle school girls reported walking to school on one or more days in a usual week in North Carolina based on the Youth Risk Behavior Surveillance Survey (YRBS).27
Few studies have attempted to compare the physical activity levels of active travelers to those who use inactive travel modes. Physical activity of walkers and non-walkers from five urban primary schools in Bristol, England were compared before and after school.11
Significant differences in 8AM to 9AM (before school) physical activity were observed between walkers and non-walkers. However, only the boys who walked to school showed higher total daily physical activity when compared to non-walkers.11
Another English study found that school travel had little or no impact on the weekly physical activity of 5 y olds in their first year in school.12
Using a different MVPA cut-point (≥1399 and ≤1547 counts per minute) a study of 13–14 y old boys and girls in Edinburgh, England, showed that students who walked both to and from school accumulated 26 minutes more of MVPA for an entire weekday than those who traveled by car, bus, or train. In our study, adolescent girls who walked before and after school accumulated 4.7 minutes more of MVPA and 13.8 more minutes of MVPA (3 MET) than the non-walkers.
Adolescents who use active means of transport to school may be less likely to be overweight or obese, according to data from the National Longitudinal Study of Adolescent Health (ADD Health) study.28
Although this speculation holds promise, only a few studies have attempted to link travel mode to this health outcome. In a recent study of Nebraska youth, Heelan and associates29
failed to find a significant association between BMI and a school travel index (times per week X distance). There was, however, a significant and positive association between self-reported physical activity and travel index. The impact of active school travel may be more important at the population level. Sturm30
suggests that if an additional 25% of children were to walk to school, total active travel time could increase by 50% in the US. In our study, there was no difference in BMI between girls who reported “travel by walking” before and after school and those who did not. However, the difference in daily minutes of MVPA for TAAG girls who reported travel by walking before and after school versus those who did not was approximately 4.7 to 13.8 minutes, depending on the definition for the MVPA threshold. The mean difference in energy expended before school between those who walked and those who did not was 194 kJ or 46 kcals/day (232 kcals/week). Alternatively, if we use 9 minutes of additional MVPA as a midpoint for this 4.7 to 13.8 minute range, this would translate into 45 additional minutes of MVPA per week. Since walking 2.5 mph expends approximately 14 kJ/min (3.35 kcal/min) in adolescent girls23
, this would translate into approximately 151 kcal/week of additional energy expenditure and approximately 0.59 kg of weight gain prevention over an average 30-week school year. Hill and Peters31
have estimated that an increase in energy expenditure of approximately 50 kcals/day would halt the increase in obesity occurring among at least 90% of adults. To our knowledge, similar estimates are not available for youth. Before and after school walking has the potential to contribute to a comprehensive plan for overall increased activity and consequently increased energy expenditure and prevent excessive weight gain.
An ancillary study of TAAG, using the same baseline data from this same sample, explored whether proximity to school was associated with physical activity by mapping the addresses and calculating the shortest distance from their home to their school along the street network.32
Of the 1,556 6th grade girls whose home addresses could be geocoded, 15.5% lived within a mile of their school; 28% lived within 1–2 miles, 23% lived 2–3 miles from school, and 33% lived 3 or more miles from school.32
In our study the mean distance to school (along a street network) for girls who walked both before and after school was 1.9 miles, compared to 2.4 miles for after school walkers, 2.7 miles for before school walkers, and 2.8 miles for non-walkers (p<0.001). Additionally, 34% of before and after school walkers lived within a mile of their school, while 23%, 20%, and 12% of the after school walkers, before school walkers and non-walkers respectively lived within a mile of school. Girls who walked before and after school also had a slightly more positive perception of their neighborhoods. The closer proximity to school as well as their perceived positive perceptions of their neighborhoods might be factors related to increased walking.
Several potential limitations of this study merit comment. First, specific questions about transportation modes to school were not included in the data collected at baseline. The post-intervention measurement occasion will include this information. Therefore, use of the “travel by walking” item on the 3DPAR within the before and after school time frame may not necessarily represent walking to school. However, by examining the “where” variable associated with each 30-min block of activity on the 3DPAR, we were able to determine that 60% of the participants who reported “travel by walking” before school identified “school” as their destination during the activity. Therefore, it is likely that girls who reported travel by walking but whose destination was not school, were simply walking to a bus stop or walking after already having arrived on the school grounds. Second, the 3DPAR asks respondents to report the activity performed for the majority of a 30-min “block” of time, not specific minutes of time. Thus, the duration of the reported activity during a block could be much less than 30 minutes. Nevertheless, a recent study found the 3DPAR to be slightly more accurate than asking middle school girls to recall exact minutes of time.21
In addition, since walkers accumulated a mean of 43.8 minutes of total physical activity and 13.3 minutes of MVPA (3 METS) before school, for example, it appears reasonable that walking may indeed have been their main activity during that time period. Another potential problem may be confounding variables (other sources of activity during the day) when testing for differences in activity. We examined group differences for potential confounding variables (i.e. the percentage of girls who participated in PE, participation in sports teams in or out of school, participation in classes or lessons taken in and out of school as recorded by the girls). After controlling for these variables, there remained a difference between those girls who travel by walking before and after school and those who did not. Also, we did not consider the economic factors that might prohibit these adolescent girls from walking before and after school. Lastly, the finding that girls who reported before and after school travel by walking also had correspondingly higher accelerometer counts before and after school than non-walkers provides strong evidence that the contextual question on the 3DPAR yielded valid scores.
Studies like this one that focus on unexplored targets for intervention among adolescent youth are important. With the continued escalation in obesity rates especially among adolescents, opportunities to alter the energy balance toward caloric expenditure must be found. Walking to and from school is a low cost and attainable physical activity. Although most efforts to promote walking occur at the elementary school level, public health and education officials should search for promotion strategies that appeal to youth in middle schools.
In this study of middle school girls, 14% reported travel by walking before school and 18% reported travel by walking after school. We found that girls who reported “travel by walking” before and after school had 4.7 more minutes of MVPA and 13.7 more minutes of total physical activity than girls who did not report this activity. Before and after school walkers also expended 194 kJ more than non-walkers. This reveals an opportunity for increasing the activity level of adolescent girls through interventions to increase the percentage of girls who use active travel to school. Though the amount of activity added may not prevent obesity, the potential for this activity to contribute to a comprehensive plan for overall increased activity and increased energy expenditure is evident.