An important component of children's total physical activity comes from extracurricular sports participation. Extracurricular sports are those organised and non-organised sports played outside of the school curriculum, and form an element of children's discretionary physical activity. Sports participation in childhood and adolescence is important because it is thought to be associated with lower levels of antisocial behaviour 12, higher levels of positive emotional wellbeing 3 and greater participation in sport in adulthood 4.

Extracurricular sports participation has substantially decreased in Australian children over the last 15 years. In 1985, 91% of boys and 90% of girls participated in at least one extracurricular sport 5, whereas in 2000 this had decreased to 71% of boys and 58% of girls participating in at least one extracurricular sport 56. Over the same period, the prevalence of childhood overweight and obesity has increased, with Australian children in 1995 being nearly twice as likely to be overweight and more than three times as likely to be obese as children in 1985 7.

With the increasing rates of childhood overweight and obesity 7, and suspected declines in levels of overall physical activity, it is important to explore correlates of children's physical activity. A recent review of these correlates recommended more research examining the inconsistent associations seen in previous studies between children's physical activity and parental physical activity 8. There have also been inconsistent findings in studies that have assessed whether the sex of the physically active parent is associated with children's physical activity 9101112. These inconsistencies are possibly due to methodological differences, which make it difficult to compare results directly. For instance, studies that have used accelerometers to objectively measure physical activity in children and their parents have found significant associations between children's and parental physical activity 91314, as have studies that have used children's reports of their parent's physical activity 101516. Studies that have used self-reported parental physical activity have generally found no associations1117181920. A number of these studies, however, had limited sample sizes 9131417, reducing the statistical power and limiting the ability to draw firm conclusions.

Few studies have explored the relationship between parental exercise and children's extracurricular sports participation and cardiorespiratory fitness levels. In the two studies that have explored this relationship 1118, no association was found between parental physical activity and children's physical fitness, as measured by maximal oxygen uptake 11 and 1-mile run time 18. However, it may be expected that parental exercise plays a role in children's physical fitness through a variety of mechanisms, including role modeling and genetic associations. No research to date has used a population-based sample, nor has this relationship been assessed in the Australian setting, which may have unique sociocultural features.

This study aimed to examine the relationship between children's extracurricular sports participation, cardiorespiratory fitness and parental exercise in a large, nationally representative sample of Australian children aged 9–15 years. We hypothesise that children who report having more active parents are involved in a greater number of extracurricular sports and have higher levels of cardiorespiratory fitness than children who report having less active parents. We also hypothesise that where only one parent is reported as active, that the sex of that parent influences children's extracurricular sport participation and cardiorespiratory fitness.

The Australian Council for Health and Physical Education Research's Australian Schools Health and Fitness Survey (ASHFS), conducted in 1985, remains the largest population-based study of children in Australia with extensive health and fitness measures and a high response rate. Due to this high response rate and population-based approach, results from this study are less likely to be subject to selection bias. Data from this study provide information on children and adolescents from a wide age range (9–15 years) and provide the opportunity to compare with current and future trends.

The findings from this study suggest that parental exercise is positively associated with children's extracurricular sports participation and cardiorespiratory fitness. Having two physically active parents was associated with participation in a significantly higher number of extracurricular sports and with significantly greater cardiorespiratory fitness, compared to having two physically inactive parents. When only one parent was active, the sex of that parent was not an independent predictor of the child's extracurricular sports participation and cardiorespiratory fitness in most instances. These associations remained after adjusting for age, SES and school type.

While the magnitude of the differences observed in the current study were small, they may still be of public health significance. In adults, clear associations have been demonstrated between physical activity and cardiorespiratory fitness and various health outcomes, including all-cause mortality 2627 and cardiovascular disease 282930. Other research has suggested that physical activity behaviours in childhood may predict physical activity behaviours in adulthood 43132. The contribution that childhood behaviours make to adult health is unclear, but it is possible that small associations such as those seen in the present study may play a role.

There are a number of possible mechanisms, also identified in other studies, through which parental exercise may influence children's extracurricular sports participation. Firstly, it is plausible that parents act as role models for children's extracurricular sports participation. When children observe that their parents are actively involved in and value sport and exercise, they may adopt these values and behaviours themselves. Secondly, a recent review of correlates of children and adolescent's physical activity found parental encouragement and support to be more strongly associated with children and adolescents' participation in physical activity than parental role modeling 8. It is possible that physically active parents provide more support and encouragement for their children to be active and influence their children's activity levels in this way. Thirdly, it may be that a genetic predisposition to physical activity exists. In a recent review, Beunen and Thomis reported that the heritability coefficients for sports participation ranged from 0.35–0.83, and that children who had a parent active in sport had 1.2–5.8 times the odds of participating in sport than children whose parents were not active in sport 33.

In the current study, an association was also seen between parental exercise and children's cardiorespiratory fitness. It is possible that by influencing children's physical activity, parental exercise may indirectly influence children's fitness. However, a recent analysis found that while more active children tended to be fitter, children's physical activity only had a modest correlation with fitness (r = 0.17) 34. It is also possible that parental fitness may influence children's fitness through genetic mechanisms. Results from studies assessing familial resemblance of cardiorespiratory fitness have found varying results, with the contribution of genetic factors ranging from 20–50% 3536.

Interestingly, our findings are consistent with the results of other studies that have used similar measures of physical activity. For instance, both Anderssen and Wold 15 and Gregson and Colley 10 measured children's physical activity using self-reported questionnaires and measured parental physical activity using a questionnaire with children. Our findings also parallel the results of studies that have used accelerometers to objectively measure physical activity in children and adults 913. However, studies that have used a parental self-report of physical activity have generally found no association between children's physical activity and parental physical activity 1116171820.

Little research has explored the reliability and validity of children's reports of their parents' physical activity. One study of 198 Grade 7–9 students found that children's report of their parents' physical activity correlated with parental self-reported physical activity at low to moderate levels (r = 0.16–0.47), except in Grade 9 girls (r = -0.01) 16. Another study of 755 Norwegian families demonstrated a moderate correlation between parents' self-reports of physical activity and their 13 year-old children's reports of parental physical activity (r 0.42–0.54, p < 0.001) 37. This suggests that the children in the current study were likely to report reasonable estimates of their parents' exercise. It is possible that children's perceptions of their parents' exercise behaviours may have a greater influence on children's physical activity than parents' exercise behaviours themselves. However, studies that have assessed parental physical activity objectively have found similar associations as the current study.

The current study found very little difference between the association of mothers' exercise compared to fathers' exercise with children's extracurricular sports participation and cardiorespiratory fitness, with the exception of a stronger association of mothers' exercise and girls' PWC₁₇₀. These findings generally suggest that as long as one parent is active, the sex of the active parent makes little difference to extracurricular sports participation and cardiorespiratory fitness, with the exception of PWC₁₇₀ in girls, where having an active mother only was associated with greater fitness than having an active father only.

These results contrast with previous research that found fathers' activity to be more influential than mothers' activity 912, mothers' activity to be more influential on girls' physical activity 1011, mothers' activity to be more influential than fathers' activity on boys' physical activity 38 and parents of the same sex as the child to have the most influence on their child's physical activity 39. These inconsistencies may be due to different definitions and assessments of children's physical activity. In the current study, the extracurricular sports component of physical activity was the main outcome factor, whereas previous studies have examined children's leisure time physical activity. Previous research has found that parents play a strong 'gate keeping' role in their children's extracurricular sports participation 18. Parents are the usual providers of transport, equipment and funding typically not required for general and school-based physical activity. It is possible that as long as one parent provides support for extracurricular activity, the sex of that parent is not important. The sex of the active parent may be more important in influencing other domains of children's physical activity, such as active play or household activity. The differences in findings between this and other studies may also be related to the differing measures of physical activity. Some measures may "capture" some activities – such as high intensity, structured activities – better than others, and it is plausible that men and women participate in different types of activities that are "captured" differently.

A limitation of this study was that regular parental exercise was defined in the ASHFS 1985 survey as two or more times per week, while guidelines dating back to the 1960s recommend physical activity on three to five days per week for health benefits 40. Although the ASHFS definition of regular physical activity may not meet current guidelines, this data still provides an estimate of those parents who participated in regular exercise and those who did not. A second limitation is that this study did not collect information on the frequency, duration or intensity of the extracurricular sports. It is possible that children who listed six sports may only participate in these occasionally, whereas children who listed one sport may participate every day for a number of hours. Additionally, children were asked to lists sports they had played "regularly" in the past year, yet a definition of "regularly" was not provided. The interpretation of this question by the children may therefore be variable. However, it was interesting to note the strong and consistent relationship seen between the number of extracurricular sports listed and both cardiorespiratory fitness measures in boys and in girls.

As evidenced in the current study, parental exercise may be important for children's extracurricular sports participation and cardiorespiratory fitness, which may influence children's health later in life. In the nationwide Active Australia survey, parents were deemed one of six population groups at risk of physical inactivity 41. Those parents with one or more children under the age of 18 living at home were 20% less likely to be considered sufficiently active than those adults without children 41. The low national levels of parental physical activity in Australia are consequently of concern. While these data are historical, we believe it would be useful for other researchers to use the data reported here to assess whether cultural changes, technological advances and increases in overweight and obesity have impacted on the apparent association between children's extracurricular sports participation, cardiorespiratory fitness and parental exercise.

The results of this cross-sectional study suggest that parental exercise may influence children's participation in extracurricular sport and their cardiorespiratory fitness. While the magnitude of the differences seen was small, these differences may be important for future health. Because Australian parents are also a group at risk of physical inactivity, targeting parents may provide health benefits for the whole family.

The author(s) declare that they have no competing interests.

VC conceptualised and drafted the paper. AV contributed to the conceptualisation of the paper, interpretation of the data and critical revision of the paper. JF provided statistical support and critical revision of the paper. TD was involved in the design, management and data collection in the ASHFS, contributed to the interpretation of the data and provided critical revision of the paper. LB provided statistical guidance and critical revision of the paper. All authors read and approved the final manuscript.