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approximations. Nevertheless, significant numbers of adolescents 13–15 years of


age throughout the world did not meet the recommendation for MVPA.


The relatively small percentages of adolescents meeting the recommendation for


MVPA were complemented by relatively high percentages of youth 13–15 years in


Europe and North America (66% boys, 68% girls, HBSC data) who spent two or


more hours per day viewing television, an indicator of physical inactivity (Hallal


et al. 2012 ). In the GSHS data for 34 countries, it was estimated that more than


one-third of adolescents spent three or more hours in sedentary activities: television,


computer games, talking to friends and other sitting activities, excluding time at


school, and doing homework (Guthold et al. 2010 ).


Accelerometry


More recent surveys based on accelerometry often focus on epochs of MVPA, the


intensity of activity that is most often associated with health benefits (Strong et al.


2005 ). Observations derived from 4 to 7 days of accelerometry in a nationally


representative sample of US youth indicate a decline in MVPA from 9 through


15 years of age in both sexes, higher levels of MVPA in boys than in girls, and


higher levels of MVPA on weekdays compared to weekend days in both sexes
(Nader et al. 2008 ). Boys exceed the recommended 60 min of MVPA at all ages


except 15 years, while girls exceed the recommendation from 9 to 13 years when


levels of MVPA fell below 60 min.


Corresponding data for European adolescents show a relatively small though


significant decline in MVPA between 13 and 17 years of age in both sexes, but


boys have more MVPA than girls through the limited age range. Time per day


sedentary (<100 counts per minute) increases, on average, across the age range, and


sex differences are small (Ruiz et al. 2011 ). MVPA and sedentary behavior do not


differ by stage of puberty; however, chronological age was not apparently con-


trolled or considered in the analysis. It would make more biological and behavioral


sense to evaluate activity and inactivity levels of youth of the same chronological


age who vary in the stage of puberty and also of youth at the same stage of puberty


who vary in chronological age.


Accelerometry data for children and adolescents 3–18 years from a number of


countries are available in the International Children’s Accelerometry Database


[ICAD] (see Sherar et al. 2011 ). Composite data of accelerometry for children and


adolescents 4–18 years of age from 20 studies in the ICAD databases indicated a


pooled mean of approximately 65 min per day in MVPA, defined as more than


2000 counts per minute adjusted for sex and age to permit comparison with data for


adults (Hallal et al. 2012 ). In another analysis of data from ICAD using different


criteria, pooled data for children and adolescents 4–18 years from 14 studies


indicated the following estimates for MVPA and sedentary time: 37±23 and


24 ±17 min per day of MVPA (>3000 counts per minute), respectively, in boys and


girls, and 345±96 and 363±96 min per day of sedentary time (<100 counts per
min), respectively, in boys and girls (Ekelund et al. 2012 ).


5 Physical Activity and Inactivity Among Children... 75

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