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Med J Aust 2000; 173 Suppl 7 August: S6-S7

The question "How active are Australian children?" is almost impossible to answer directly because measuring physical activity among children is so difficult. There are many ways of estimating participation in physical activity, each with a different degree of accuracy and cost. Not surprisingly, there is a strong correlation between cost and accuracy. For population surveys, the only method with acceptable cost is to ask respondents to self-report their physical activity habits. Unfortunately, children under about 11 years of age lack the cognitive skills required to report their activities accurately. Alternatively, we could measure cardiovascular endurance using a field test like the 20-metre shuttle run, but this approach also has some difficulties -- in particular, making decisions about appropriate cut-off values (how fit is fit enough?).

As a consequence of such measurement difficulties, we have to resort to one of two indirect approaches. The first is to take accurate measurements on small numbers of children and attempt to extrapolate to the population (a high-risk strategy); few data of this kind exist. The second is to collect self-report data from older children and to extrapolate to younger ones. The NSW Schools Fitness and Physical Activity Survey, 1997, collected self-reported physical activity data on students in Years 8 and 10 in schools all over NSW and found that approximately 80% of Year 8 students were sufficiently active.²⁴ We would not expect a substantial increase in physical activity between primary school and Year 8, so it seems reasonable to assume that about 80% of Australian children are sufficiently physically active. This figure is roughly consistent with the report by Baur in this supplement (question 7), who estimates that about 25% of children are overweight or obese.

Thus, it seems that a very substantial minority of children (probably 20%-25%) are not physically active and are probably also overweight. They are at increased risk of becoming inactive and overweight adults, are likely to have developed atherosclerotic lesions by the end of the second decade of life, and are at increased risk of developing diabetes.

Children who are sufficiently active, particularly those who participate in vigorous-intensity sports at least 3-4 times per week, enjoy a lower risk of developing "lifestyle diseases" later in life and are also laying the foundations of a healthy adult lifestyle.

In the absence of formal activity guidelines for children, the best advice for parents is:

• Provide daily opportunities for children to be active, in a variety of ways, in a safe environment;

• Avoid driving children on short trips when walking is possible;

• Limit the time children are permitted to spend in sedentary recreation such as watching television and playing computer games to, say, 30 minutes a day;

• Support children's development of fundamental movement skills by playing games with them, encouraging them to play sport, and by asking your child's school to implement the Fundamental Movement Skills curriculum.

Michael L Booth

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