One of the problems in assessing the prevalence of physical inactivity (and therefore the estimation of the PAR) is that it is difficult to define physical inactivity. Most of the time, physical inactivity is defined as ‘not reaching the guidelines for healthy physical activity’.
However in the beginning of the 1990s, Cale & Almond (1992) reviewed 15 studies conducted on British children and reported that children seldom participate in activity at a level that would have a cardiovascular training effect or a health benefit.
On the other hand, in the same period, Sallis examined nine studies and concluded that the average child is sufficiently active to meet the adult recommendations for conditioning activities, with the exception of the average girl in mid to late adolescence (Sallis 1993). It has further been noted that young children are highly and spontaneously active and that children are generally fitter and more active than adults and most of them are active enough to receive important health benefits from their activity.
In the United Kingdom, around 70% of boys and 61% of girls, aged between 2 and 15 years, meet the recommended level of 1 hour of physical activity each day (including sport and organized exercise, active play, walking, gardening or housework). For girls, however, participation in physical activity declines after about 11 years of age, so that by age 15 years, only 50% undertake an hour of physical activity each day (Department of Health 2003). On the other hand, from longitudinal studies there is also evidence that for both boys and girls during especially the adolescent period, there is a (huge) decrease in physical activity levels, which continues into the adult period.
Another way of looking at the prevalence of physical inactivity is to look at the prevalence of sedentary behaviours such as television viewing, computer use or video game playing. Survey data from the USA, for instance, show that up to a quarter of American children aged between 8 and 16 years watch more than 4 hours of television each day (American Academy of Pediatrics 2003). However, the amount of time spent watching television and playing video games is not inversely correlated to the amount of time spent in physical activity.
There is some evidence that the level of physical activity of children and adolescents is lower than that of similarly aged children a few years ago. This is mainly based on the finding that the caloric intake today is lower than the caloric intake in previous generations, and yet the previous generations were less fat. This can only be caused by a decrease in physical activity. This secular trend observed for physical activity levels of children and adolescents suggests the importance of this age period for interventions aimed at an improvement (or maintenance) of physical activity levels.
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