(one mile run, pull-ups, sit-ups, sit and reach, skinfold thickness) and physical
activity (accelerometry, parental report, child self-report) in about children 9–
10 years (Sallis et al. 1993 ) were generally low. After controlling for age and sex,
physical activity accounted for only 3–11% of the variance in the indicators of
physicalfitness considered. Similarly, correlations between sedentary time and time
in light, moderate, moderate-to-vigorous, and vigorous physical activity based on
accelerometry and aerobicfitness (peak VO 2 ) were low in among 6–7-yearold boys
and girls (Dencker et al. 2010 ). Total accelerometer-based physical activity
accounted for 3% of the variance in aerobicfitness in boys and none of the variance
in girls, but the percentage of time in moderate physical activity accounted for 8%
and 2% of the variance in aerobicfitness in boys and girls, respectively.
Indicators of physical activity are related to aerobic and/or cardiorespiratory
fitness (Schmücker et al. 1984 ) and other components of health-relatedfitness
(Katzmarzyk et al. 1998 ) among adolescents. More recent observations based on
accelerometry noted significant but low relationships between MVPA and aerobic
fitness in adolescent boys and girls 13–16 years which varied with area of residence
—urban or rural (Machado Rodrigues et al.2012b). Further data suggest inde-
pendent associations between physical activity and sedentary behavior and car-
diorespiratoryfitness among youth 10–18 years (Santos et al. 2014 ).
Relationships between physical activity andfitness, though statistically signifi-
cant, is not strong among children and adolescents. This reflects in part the different
measures of physical activity andfitness used in the studies. Nevertheless, most of
the variance infitness is not accounted for by physical activity, which implies that
factors other than activity influence thefitness of youth. As in the discussion of
motor proficiency and activity, there is a need to include other factors in analyses of
physical activity and physicalfitness. Moreover, several indicators of physical
fitness have well-defined growth spurts which vary relative to the growth spurt in
height. On average, measures of static strength and power attain peak gains after
peak height velocity, while peak gains in maximal aerobic capacity (VO 2 max)
occur coincident with peak height velocity in both sexes (Beunen and Malina 1988 ;
Geithner et al. 2004 ; Malina et al. 2004 ).
Correlates of Physical Inactivity
Time watching television and videos is a commonly used indicator of inactivity.
Limited data (Van der Horst et al. 2007 ) suggest that having an elevated BMI and
being depressed are associated with more time in these two physically inactive
behaviors among adolescents. Being a male is also a risk factor as boys spend more
time watching television and videos than girls. The data also suggest variation in
physically inactive behaviors associated with ethnicity, socioeconomic status, and
parental education. Adolescents who are non-White and of lower socioeconomic
status, and have parents with less education, are more likely to be physically
inactive.
5 Physical Activity and Inactivity Among Children... 87