School physical activity has a range of intended benefits including improved motor skills, fitness, social interaction and learning . Policies that make school physical activity compulsory are also seen as an opportunity for health promotion through increasing children's overall energy expenditure and thereby reducing the risk of obesity. This study aimed to examine whether children who attended schools that reported higher levels of compulsory physical activity had higher levels of physical activity and cardiorespiratory fitness and a lower prevalence of overweight than children who attended schools reporting lower levels of compulsory physical activity. Overall, the findings suggest that the amount of compulsory school physical activity reported had little effect on children's total physical activity and fitness and on the prevalence of overweight and obesity. However, children at schools providing more compulsory school physical activity tended to report more school-based physical activity than children at schools providing less compulsory physical activity.
Our cross-sectional findings for children are consistent with some previous research. A study of children (n = 215) at three schools in England found that irrespective of the time spent in physical activity at school (9, 2.2 or 1.8 hours per week), there was no difference in children's total physical activity as measured by accelerometer . Similarly, a two-year Nebraskan trial found that children (n = 338 at baseline) who received enhanced physical activity (30–40 minutes 3 days per week), grade specific nutrition education and a modified school lunch program had classroom physical activity levels 6% higher than controls, but outside of school physical activity was 16% lower, and no significant differences in body mass index (BMI) were noted in a subsample (n = 108) . In contrast, a South Australian school-based physical activity trial observed increases in children's fitness (n = 513) and decreases in body fat (n = 510) following an intervention that included 6.25 hours (375 minutes) of high intensity, structured physical activity per week . In the current study, schools provided a median of 2.67 hours (160 minutes) per week. This suggests that larger amounts of school-based physical activity conducted at high intensities under strict intervention conditions may be required to see differences in total physical activity, fitness and body mass.
Attending a school that reported higher levels of compulsory physical activity was not associated with adult physical activity, cardiorespiratory fitness or weight status. To our knowledge, this is the first study to investigate the long-term effects of compulsory school physical activity under non-intervention conditions. One Canadian study followed up 147 children 20 years after they received a specialist-taught PE intervention from grades 1 through 6 . Similar to the current study, no significant differences in adult adiposity in either sex or physical activity levels in males were observed, although a higher proportion of females in the experimental group (35.5%) reported participating in strenuous physical activity three or more times per week, compared with the comparison group (20.2%) . Our findings are consistent with the generally low levels of tracking observed between child and adult physical activity (r = 0.05–0.54) . While it is of public health interest to examine the long-term impacts of childhood exposures (such as exposure to higher school physical activity provision), there are a large number of external influences on physical activity behaviors during childhood, youth and young adulthood [27, 28] that may override any effects of school physical activity provision.
Our study had some limitations. Children's self-reported physical activity is prone to measurement error  which may bias findings towards the null. However, this seems unlikely to have substantially affected our results because objectively measured cardiorespiratory fitness, which closely reflects an individual's physical activity levels, demonstrated similar associations. Also, children's self-reported physical activity was reported at levels consistent with those observed in other studies [30, 31] and was correlated with cardiorespiratory fitness at similar levels to that observed previously (Spearman's rho = 0.17) [32, 33]. While measurement of adult levels of physical activity can also be problematic, we attempted to overcome this by using both self-reported and objective measures, which have been shown to be validly and reliably used in large population-based studies [16, 17, 34–37]. Average values for self-reported total physical activity were similar to those reported in other studies using the IPAQ-L , and average daily steps were similar to those observed in an Australian study of 18–29 year olds , although studies in other populations have demonstrated lower  and higher  average daily step values. These measures however do suffer from limitations; the IPAQ-L has been criticized for overestimating physical activity , while pedometers are unable to capture non-ambulatory activities such as swimming, cycling or weight-training. School-reported physical activity and child-reported physical activity were not well-correlated; school reports of compulsory physical activity provision may also have been prone to measurement error. This could have resulted, for example, from different amounts of school physical activity being provided to different grades or from the effects of social desirability prompting schools to over-report their school physical activity.
A limitation of the follow-up analyses is that only 28% of the original sample had follow-up measurements. While there were some small sociodemographic differences at baseline (as described in the Results), there were no significant differences in physical activity or cardiorespiratory fitness values at baseline between those who participated in follow-up and those who did not. The prevalence of overweight at baseline was lower in those who participated in follow-up although the adult sample had similar levels of overweight and obesity to Australians of the same age [19, 20]. Whether an association between school physical activity provision in childhood and adult physical activity, fitness and overweight is different in those who did not participate is unknown.
A range of unmeasured factors such as school resources, interest and parental expectations may have contributed to schools' compulsory physical activity policies in 1985. These could be potential confounders in the association between school physical activity provision and our outcome measures of physical activity, fitness and overweight. Also, the degree to which findings from 1985 translate to present day school environments is not clear. Nevertheless, given that no other national dataset of this nature and size currently exists in Australia, and no previous studies have examined long-term influences of compulsory school physical activity on adult physical activity, fitness and overweight, this study is uniquely placed to contribute to debate about the likely benefits of compulsory school physical activity. This study also has key strengths in its size, length of follow-up, extensive range of behavioral and biological measures and ability to adjust for a range of potentially confounding factors.
While compulsory school physical activity may bring a range of physical and social benefits to children  our findings suggest that policies promoting or requiring compulsory physical activity of up to 190 minutes per week in primary schools and 220 minutes per week in secondary schools may be insufficient to increase total physical activity and fitness levels or decrease the prevalence of overweight in childhood or in the longer term.