THE HEALTH-RELATED PHYSICAL-ACTIVITY OF CHILDREN

The fitness and physical activity levels of children and youth are com monly questioned, but the evidence cited is both equivocal and methodo logically diverse. The amount and type of physical activity undertaken during childhood that is appropriate for optimal health is unknown, a lthough it has been suggested that, in the absence of such criteria, a ctivity levels known to confer health benefits in adults are also appr opriate for children. The measurement of activity in children is probl ematical, and there is currently no valid method of assessing activity levels that is feasible for use in large studies. Therefore, studies may lack either internal validity or wider applicability. Studies usin g self-report methods indicate relatively high levels of activity with 60 to 70% of children taking sufficient ''appropriate'' physical acti vity, However, a variety of activity thresholds have been used, Studie s that use more objective methods report much lower levels of activity , especially when cardiovascular fitness criteria are applied. The use of less stringent health-related thresholds results in higher levels of ''appropriate'' activity, Nearly all studies of teenagers report a decline in activity with age during this period. Data from the large p opulation studies indicate that activity levels peak in children at ar ound 13 to 14 years of age, and then markedly decline. Boys are normal ly reported to be more active than girls, but this difference is great ly reduced when moderate activity alone is compared, indicating that b oys participate in more vigorous exercise than girls. The health effec ts of low levels of vigorous activity in children are unclear. There i s a need to identify more clearly the quantity and type of activity wh ich is appropriate for children's health and well-being, and to improv e assessment techniques. There is a particular need to assess the valu e of, and measure the prevalence of, low to moderate intensity activit y below the level normally considered appropriate for cardiorespirator y fitness improvement.