of sexual maturation and the adolescent spurt. Several outcomes of interest (e.g.,
bone mineral content, aerobicfitness, HDL-C, adipose tissue, muscular strength)
have their own growth patterns, and some have reasonably well-defined ado-
lescent spurts which vary in timing (Malina et al. 2004 ).- Inter-individual variation in response to activity intervention and experimental
protocols needs further study. For example, peak VO2 increased, on average,
from 44.7 to 47.6 ml/kg/min after a 12-week aerobic training protocol in a
sample of 35 boys and girls 10.9–12.8 years of age (Rowland and Boyajian
1995 ). The mean relative gain was 6.5%, but changes in individuals ranged from
−2.4 to +19.7%. - The beneficial effects of physical activity on indicators of health appear to
differentiate to some extent between“healthy”and“unhealthy”youth. Among
“healthy”children and adolescents (i.e., normal weight, normotensive blood
pressure), the evidence base is strongest for skeletal health, aerobicfitness, and
muscular strength and endurance, with relatively small effects on lipids, adi-
posity, and blood pressures. On the other hand, physical activity programs have
a beneficial effect in“unhealthy”youth—on adiposity in the obese, blood
pressures in the hypertensive, and insulin, triglycerides, and adiposity in obese
youth with clustered cardiometabolic risk. - Many indicators of health andfitness, in particular cardiometabolic risk factors,
are affected by obesity. A key issue is the prevention of“unhealthy weight gain”
in youth. Given the individuality of growth rate and the timing and tempo of
growth and maturation during the adolescent growth spurt, it may be difficult to
specify“unhealthy weight gain.”The maintenance of smaller gains in the BMI
through physical activity over time may help to prevent unhealthy weight gain
and in turn reduce risk of overweight/obesity and associated complications.
Closing Comments
Many forms of physical activity and inactivity are important behaviors in the daily
lives of children and adolescents. They have implications forfitness and health,
learning, enjoyment, social interactions, and physical and psychological develop-
ment. Physical activities are also central to behaviors essential to subsistence in
many parts of the developing world, and children and adolescents have expected to
contribute to these efforts. Physical activity and inactivity are independent behav-
iors performed in a societal context, and many have high valence in societies. There
is a need for better understanding of meanings attached to and motivations for
physically active and sedentary behaviors, and of potential correlates—demo-
graphic, biological, psychosocial and cultural, and their interactions.
5 Physical Activity and Inactivity Among Children... 91