Table 6 provides OR for fitness categorization by travel mode calculated by logistic regression. Girls who walked to school were more likely to be classed as fit (OR = 1.31, 95% confidence interval (CI) = 1.03-1.66, P = 0.027) compared with those who used passive transport, and girls who cycled had nearly 10 times the odds for being fit (OR = 9.99, 95% CI = 1.30-76.59, P = 0.027). Compared with those who used passive transport, boys who walked were more likely to be classified as fit (OR = 1.20, 95% CI = 1.00-1.43, P = 0.045), as were cyclists (OR = 1.31, 95% CI = 1.00-1.72, P = 0.049). OR for PA-adjusted fitness categorization by travel mode are reported in Table 6. The OR for being fit in girls who walked to school changed very little (OR = 1.34, 95% CI = 1.05-1.71, P = 0.018). The OR were reduced slightly in girls who cycled, but these girls were still eight times morel likely to be classified as fit compared with passive transport users (OR = 7.94, 95% CI = 1.05-60.23, P = 0.045). In boys, however, there was no significant association between travel mode and fitness category after adjusting for PA.
Travel mode and aerobic fitness.
Cycling to school is associated with better aerobic fitness in Danish schoolchildren (1,9,10). The aim of the present study was to determine whether school travel mode is associated with aerobic fitness in English schoolchildren. In common with previous studies (1,9,10), girls who regularly cycled to school had significantly higher mean aerobic fitness test scores when compared with public transport and car users. All girls, except for one, who cycled to school were categorized as fit, a significantly greater proportion than in any other travel mode group. Girls who cycled were 10 times more likely than passive transport users to be classified as fit (OR = 9.99, 95% CI = 1.30-76.59). The large CI in the female cyclists' group were mainly due to the low number of individuals in this group (n = 71). Similarly, boys who cycled had a higher mean aerobic fitness test score when compared with boys that were driven to school. In agreement with previous studies (1,9,10), male cyclists were significantly more likely to be classed as fit compared with passive transport users.
No previous data have demonstrated an association between walking to school and aerobic fitness. In the present study, however, girls and boys who regularly walked to school were fitter than those who were driven. Boys and girls who walked to school were also significantly more likely to be categorized as fit compared with passive transport users.
The present data agree with existing literature in showing that cycling to school is associated with higher levels of aerobic fitness but are the first to show such an association with walking to school. The novelty of this finding is most probably the result of differing national travel habits, but the possibility remains that methodological differences in the assessment of aerobic fitness may have also had an impact. The predominant travel mode to school in Denmark is cycling, where cycling is positively associated with aerobic fitness (1,9,10). In the present English sample, however, the predominant mode of transport is walking. The current data do show that walkers were fitter than passive transport users. Cyclists were, however, fitter still. Commuter cycling tends to be a more intense form of exercise than walking. These data, therefore, support the previous suggestion (10) that exercise intensity of the active commuting mode may play a role in the strength of the association between travel mode and aerobic fitness.
Reported school travel habits were broadly similar to UK national averages (13), except that walking and cycling were slightly overrepresented. All existing data showing associations between cycling to school and aerobic fitness (1,9,10) come from schoolchildren in Denmark (Danish Youth Heart Study, European Youth Heart Study), where two-thirds of adolescents regularly cycle to school. Denmark has good infrastructural provision and a strong culture of cycling (10). Cycling to school is rare in the United Kingdom (13) and even less common in the United States (19) and Australia (31). The relative infrequency of cycling necessitated the large overall sample size of this study (n = 5927). Previous studies may have had larger relative and absolute samples of cyclists, but the present data allow more powerful analysis of aerobic fitness of walkers and public transport users.
Participants of the present study were broadly similar to English reference data (34) in the prevalence of overweight and obesity: roughly a quarter of children and adolescents were overweight and obese. These rates are much greater than those seen in Denmark, where only a sixth of children and adolescents are overweight and obese (18). This may allow some generalization of the present findings to countries such as the United States and Australia, where active school travel by bicycle is low, and the obesity epidemic and associated health burdens are equally prevalent.
Aerobic fitness versus PA as a marker of health.
Several studies have shown a positive association between active travel to school and PA levels in children (7,8,27) and adolescents (30). Some studies (9,10) have reported conflicting data with regard to the association between PA and school travel mode. Cyclists have been reported as being less physically active than walkers yet still having higher aerobic fitness. Such a paradox illustrates the challenges associated with measuring PA in schoolchildren. In particular, it demonstrates the difficulty in estimating the PA of cyclists via accelerometry.
Aerobic fitness in children and adolescents is arguably a better marker of health than PA because of its strong associations with adiposity, current and future cardiovascular health, and psychological well-being (23). Poor aerobic fitness in children and adolescents is strongly associated with the clustering of cardiovascular disease risk factors (2) and metabolic risk (25). In addition, the objective assessment of aerobic fitness in children and adolescents is less challenging than objectively assessing PA. In this respect, it is perhaps surprising that the present data add to only a few studies (1,9,10) that have investigated associations between travel mode and aerobic fitness. As in other studies (14,28), the present study did not identify any associations between travel mode and BMI.
Measurement of aerobic fitness.
All associations between school travel and aerobic fitness (1,9,10) have been shown using maximal cycle ergometry tests, which have some obvious advantages. Maximum power output corrected for body mass (9,10) is a valid and reliable way to assess maximum aerobic fitness in adolescents (24). It has been suggested that most Danish children and adolescents are accustomed to regular cycling, even if they do not commute to school by bike (10). Because of this, it is unlikely that noncycle commuters were disadvantaged by cycle ergometry in previous studies. In England, however, cycling to school is much less common, and recreational cycling habits in this sample are presently unknown. Cycle ergometry would, therefore, be inappropriate as a method to assess aerobic fitness in the present sample. The present study assessed aerobic fitness using the 20-mSRT. The test uses running, which is an exercise modality that all children and adolescents are accustomed to. The test is a valid (16,17,32) and easily administered field test that provokes a maximal effort in schoolchildren (33). It is extensively used to assess aerobic fitness of children and adolescents (22,29). Global normative data exist for the 20-mSRT performance allowing representation of test scores as z-scores relative to a global mean (22). Danish adolescents perform better in the 20-mSRT than the global mean (22), whereas the performance of the present sample was much closer to the global mean (Table 2), thus adding to the generalizability of the present sample.
Active travel to school and health.
Previous data (10) show that schoolchildren who cycle to school are more likely to be fit than those that use passive transport. The present study adds to the existing data in demonstrating that not only cycling but also walking is associated with an increased likelihood of being fit (Table 6). More importantly, perhaps, the present study does not use arbitrary cut points to define fitness categories. Existing 20-mSRT cut points (21) were used, which are directly associated with adult health (11). Schoolchildren who were categorized as fit in the present study may enjoy a reduced risk for developing chronic disease in adulthood. Using such criteria, however, also has drawbacks. The observed associations between travel mode and fitness were notably weaker than those reported previously (10), with some relatively small OR and 95% CI approaching 1.0 (Table 6). These are likely the result of the fitness classification criteria applied. The unfit category in the present study roughly corresponds to performance predictive of the bottom quintile of adult fitness, whereas previous data (10) classified low fitness on the basis of belonging to the lowest quartile within the study population. The criteria used presently may have reduced the strength of some associations. The meaningfulness of such cutoffs in generalizability of results, however, justifies their use.
PA as a potential mechanism.
In agreement with previous studies (7,8,27,30), cyclists were more physically active than pupils using other transport modes (Tables 4 and 5). In boys, the OR for active commuters being classed as fit was nonsignificant after adjusting for this higher PA (Table 6). It may be, therefore, that active school commuting is linked to higher fitness in boys via higher levels of overall PA. In girls, however, the association between travel modality and fitness remained largely unchanged when controlling for PA (Table 6), which suggests that travel was associated with fitness independently of PA. This may be because girls reported lower overall PA than boys, and as a result, the PA associated with active school commuting contributes directly to increased fitness in girls. Investigations on potential between-sex differences in the mechanism by which active school travel is associated with fitness, either independently of or via PA, are warranted. In the present study, PA was derived from 7-day recall, which has numerous associated limitations. However, a noteworthy strength of the current measure is that the PAQ score is largely independent of any contributions from active commuting: school travel is not assessed, and daily cycling and/or walking each account for less than a percent of the total PAQ score.
Limitations and recommendations.
The present sample was not randomly selected or nationally representative. The sample was designed to represent the East of England in ethnicity, deprivation, and rural/urban mix. This region is, in turn, representative of the United Kingdom in ethnicity and rural/urban mix but is more affluent than the UK average. The sample also lacks large numbers of children from within large-city areas (defined as a population of >250,000), which reduces the generalizability of the present findings to such populations.
Total and relative frequencies of cycling were low in the present study compared with previous studies, despite a much larger sample size. This was particularly evident in girls, where this created large CI in the logistic regression analysis (Table 6). Only 2.5% of girls regularly cycled to school, and although this number seems low, it should be borne in mind that the rate is greater than the UK national average for girls (1%) (13). The phenomenon of low numbers of schoolchildren cycling to school (particularly girls) in the United Kingdom warrants further investigation.
As noted previously, PA was assessed by a 7-day recall, which has obvious limitations. The questionnaire only provides a general estimate on the basis of self-report and does not provide any objective measurements. The PAQ was, however, specifically designed to enhance participants' recall ability and has been deemed a valid and reliable tool to estimate PA in large populations (15).
Naturally, because of the cross-sectional nature of the present study design, the direction of causality of the presently identified association between active travel to school and better aerobic fitness cannot be commented on. The present study does, however, provide some insight into possible mechanisms underlying this association and some potential differences between boys and girls. Further studies aimed at elucidating the mechanism by which active travel is associated with schoolchildren's fitness are required. Mean aerobic fitness and likelihood of being fit were higher in cyclists than in walkers; this supports previous speculations (10) that exercise intensity may be a mediating factor in this association. In light of the present findings, the efficacy of this theory clearly needs to be investigated further in boys and girls.
The present data report higher aerobic fitness in cyclists compared with passive transport users in schoolchildren outside Denmark. The present study population is more representative of other western countries, such as the United States and Australia, in school commuting habits and progression of the obesity epidemic than Denmark. Present findings thus allow better generalization to such countries. The present study also shows higher aerobic fitness in schoolchildren who walk to school compared with passive transport users. Regular cycling and walking to school were significantly associated with higher mean aerobic fitness test scores. More importantly still, the present data provide a link between active travel to school and future health outcomes. Cycling and walking to school significantly increased the odds for being fit, and the cutoff used to define fit was directly linked to a reduced risk to develop chronic diseases in adulthood. The association between active travel to school and fitness, especially cycling, was particularly evident in girls. These data suggest potential mechanisms through which this association is achieved. There were between-sex differences in the role of PA. Boys who actively commuted seemed to be fitter as a result of higher overall PA, whereas in girls, the association between active travel and fitness was independent of PA. Regardless of the underlying mechanisms, the positive associations between active travel and fitness are so strong that cycling should be encouraged, especially in girls.
This study was funded by the University of Essex Research Promotion Fund and was not externally reviewed. The results of the present study do not constitute endorsement by American College of Sports Medicine.
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Keywords:©2010The American College of Sports Medicine
CYCLING; COMMUTING; PHYSICAL FITNESS; PHYSICAL ACTIVITY