Young people's physical activity patterns as assessed by heart rate monitoring.

Physical activity is a complex behaviour and the accurate assessment of young people's physical activity patterns is extremely difficult. Ideally, a combination of different techniques should be used. For example, the simultaneous use of doubly labelled water, heart rate monitoring and structured observation would yield information on total energy expenditure, patterns of relative physiological load (intensity) on the cardiopulmonary system, and the frequency, duration and type of physical activity experienced. However, the choice of method(s) is likely to be dictated by cost and logistics and heart rate monitoring alone has provided some valuable insights into young people's physical activity patterns. Sustained periods of moderate to vigorous physical activity are not characteristic of either children's or adolescents' physical activity patterns. Boys appear to be more active than girls from an early age and, although both males and females generally reduce their level of physical activity as they move from childhood through adolescence and into adult life, the rate of decline is greater in girls. Some children and adolescents are physically active, but many young people have adopted sedentary lifestyles.