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participation in physical activity and corresponding physical fitness begin to 
decline (Duncan et al., 2007). Such differences across stages of development 
highlight the importance of examining the effects of growth and maturation 
on physical and cognitive health. Accordingly, this chapter reviews how 
physical activity may influence developmental processes and other aspects of 
somatic growth and maturation. A complete review of the effects of physical 
activity on all tissues and systems is beyond the scope of this report. Rather, 
the focus is on components of body composition and systems that underlie 
engagement in physical activity, physical fitness, and chronic disease risk 
and that in turn influence other aspects of health and academic performance 
(discussed in Chapter 4). Addressed in turn is the relationship between 
physical activity and physical, psychosocial, and mental health. Structural 
and functional brain maturation and how physical activity may influence 
those developmental processes and cognitive health are also reviewed in 
Chapter 4.
PHYSICAL HEALTH
This section reviews what is known about the relationship between 
physical activity and (1) somatic growth, development, and function and 
(2) health- and performance-related fitness.