Corresponding data for adolescents span variable time intervals, are based on
self-report, and use variable criteria for activity levels. The Youth Risk Behavior
Study (YRBS, Centers for Disease Control and Prevention, now labeled the Youth
Risk Behavior Surveillance System) is a major source of data for American high
school youth, but criteria for activity are variable. A slight decline was noted in
physically active boys (“exercise and sports activities that make you sweat and
breathe hard for 20 min or more on three or more days in the past week”) between
1993 and 2003, 75–70%, but not in girls, 56–55% (Adams 2006 ). In contrast, no
change was noted in percentages of boys and girls reporting moderate (“did not
make students sweat or breathe hard”) and vigorous (“made students sweat or
breathe hard”) physical activity between 1993 and 2005 (Li et al. 2010 ). Moderate
activity did not appreciably differ between boys (29%) and girls (24%), while
vigorous activity was higher in boys (72–75%) than girls (56%).
Guidelines in the USA have since been modified to include both aerobic
(60 min per day, 7 days per week) and muscle strengthening (3 days per
week) activities (US Department of Health and Human Services 2010). In the 2010
National Youth Physical Activity and Nutrition Study, small percentages of boys
(22%) and girls (8%) met the aerobic criteria (“increased your heart rate and made
you breathe hard for some of the time”), while more youth (boys 65%, girls 37%)
met the muscle strengthening criteria (“such as push-ups, sit-ups, or weight lift-
ing”). Only 19% of boys and 6% of girls met the criteria for both (Fulton et al.
2011 ). Results for muscle strengthening were similar to the 2003 YRBS, while
those for aerobic activities were consistent with the 2009 YRBS.
Similar trends over time were apparent in European youth. Percentages of
Finnish boys and girls participating in leisure time MVPA did not vary appreciably
between 1977 and 2005, but more boys participated than girls (Telama and Laakso
2009 ). Vigorous physical activity at least four times a week did not change between
1986 and 2002 in nationally representative samples of 11–15-year-old boys and
girls in six of seven European countries; Finnish youth in this compilation showed a
slight increase over time (Samdal et al. 2007 ). Surveys of Iceland youth 14–
15 years indicated a 7–8% increase in vigorous activity between 1992 and 1997,
but negligible changes between 1997 and 2006 (Eiồsdóttir et al. 2008 ).
In contrast to US and European youth, higher percentages of South Australian
youth of both sexes reported vigorous physical activity (makes“you huff and puff
and lasts at least 30 min” in most weeks) in 2004 compared to 1985. Boys,
especially the most active, also increased in total leisure time activity in the pre-
vious week, while girls did not (Lewis et al. 2007 ). Percentages of Australian youth
12 – 15 years in New South Wales also reported increased time in MVPA between
1985 and 2004 (Okely et al. 2008 ).
5 Physical Activity and Inactivity Among Children... 77