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Educating the Student Body
interventions in overweight children and adolescents commonly combine 
exercise and dietary restriction, making it difficult to disentangle their 
independent effects. Nonetheless, diet and exercise have different effects on 
body composition: While both contribute to fat loss, only exercise increases 
muscle mass and thus has a direct effect on metabolic health. In children 
and youth, as in adults, the effect of exercise on cardiometabolic risk fac-
tors is greater in overweight/obese youth than in their normal-weight peers 
(Kang et al., 2002; Lazaar et al., 2007). 
Exercise also may have important benefits even without significant 
modification of body composition (Bell et al., 2007). Experimental studies 
in overweight and obese youth have shown that exercise leads to reductions 
in visceral fat (Owens et al., 1999; Gutin et al., 2002; Lee at al., 2005; 
Barbeau et al., 2007; Kim and Lee, 2009) without a significant change in 
BMI, as well as improvement in markers of metabolic syndrome, primarily 
fasting insulin and insulin resistance (Treuth et al., 1998; Ferguson et al., 
1999; Carrel et al., 2005; Nassis et al., 2005; Meyer et al., 2006; Shaibi et 
al., 2006; Bell et al., 2007). Results from experimental studies of the effects 
of exercise on lipids and lipoproteins (Stoedefalke et al., 2000; Kelley and 
Kelley, 2008; Janssen and LeBlanc, 2010) are mixed. Although some studies 
have shown improved lipid and lipoprotein profiles, primarily a decrease 
in low-density lipoprotein (LDL) cholesterol and triglyceride concentra-
tions and an increase in HDL cholesterol (Ferguson et al., 1999), other 
studies have shown no improvement in these outcomes (Kelley and Kelley, 
2008). In part, such conflicting results are likely due to initial differences in 
body composition and severity of hyperlipidemia. Well-controlled exercise 
training studies in obese children (Escalante et al., 2012) and children with 
adverse blood lipid and lipoprotein profiles have shown positive alterations 
in their profiles (Stoedefalke et al., 2000), whereas results in normolipid-
emic children and adolescents are equivocal. Similarly, exercise has little 
effect on resting blood pressure in normotensive children and adolescents 
(Kelley and Kelley, 2008), whereas reductions in resting systolic and some-
times diastolic pressures have been reported in youth with high blood pres-
sure (Hagberg et al., 1983, 1984; Danforth et al., 1990; Ewart et al., 1998; 
Farpour-Lambert et al., 2009; Janssen and LeBlanc, 2010).
In adults, physical activity is inversely associated with low-grade 
inflamma tion (Wärnberg et al., 2010; Ertek and Cicero, 2012), which is now 
recognized as a significant feature of metabolic syndrome and an indepen-
dent predictor of cardiometabolic disease (Malina, 2002). In obese children 
and adolescents, as in their adult counterparts, elevation of inflammatory 
markers is evident, and observational studies have shown significant rela-
tionships among physical activity, physical fitness, and inflammation (Isasi 
et al., 2003; Platat et al., 2006; Ruiz et al., 2007; Wärnberg et al., 2007; 
Wärnberg and Marcos, 2008). These relationships are better studied and 

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Copyright © National Academy of Sciences. All rights reserved.
Educating the Student Body: Taking Physical Activity and Physical Education to School
Relationship to Growth, Development, and Health
 
129
stronger in adolescents than in children. In one study of boys and girls aged 
10-15, those who were obese and unfit had the highest levels of systemic 
inflammation, whereas those who were obese yet fit had levels as low as 
those who were lean and fit (Halle et al., 2004). In another study, low-grade 
inflammation was negatively associated with muscle strength in overweight 
adolescents after controlling for cardio respiratory fitness, suggesting that 
high levels of muscle strength may counter act some of the negative conse-
quences of higher levels of body fat (Ruiz et al., 2008). Experimental studies 
of the effects of exercise and markers of low-grade inflammation in children 
and adolescents are lacking. Improved cardio respiratory fitness in adults 
(Church et al., 2002), however, has been shown to be inversely related to 
concentration of C-reactive protein (CRP), a marker of low-grade inflam-
mation. In a small study of a lifestyle intervention entailing 45 minutes of 
physical activity 3 times per week for 3 months, a small reduction in body 
fat and an overall decrease in inflammatory factors (CRP, interleukin [IL]-6) 
were seen in obese adolescents (Balagopal et al., 2005).
Performance-Related Fitness
Speed, muscle power, agility, and balance (static and dynamic) are 
aspects of performance-related fitness that change during body develop-
ment in predictable ways associated with the development of tissues and 
systems discussed above (Malina et al., 2004). Running speed and muscle 
power are related, and both depend on full development of the neuro-
muscular system. Running speed and muscle power are similar for boys and 
girls during childhood (Haubenstricker and Seefeldt, 1986). After puberty, 
largely because of differences in muscle mass and muscle strength, males 
continue to make significant annual gains, while females tend to plateau 
during the adolescent years. Sociocultural factors and increasing inactivity 
among girls relative to boys, along with changes in body proportion and a 
lowering of the center of gravity, may also contribute to gender differences 
(Malina et al., 2004).
Balance—the ability to maintain equilibrium—generally improves from 
ages 3 to 18 (Williams, 1983). Research suggests that females outperform 
males on tests of static and dynamic balance during childhood and that this 
advantage persists through puberty (Malina et
 al., 2004). 
Motor performance is related in part to muscle strength. Increases in 
muscle strength as a result of resistance exercise were described above. A 
question of interest is whether gains in strength transfer to other perfor-
mance tasks. Available results are variable, giving some indication that 
gains in strength are associated with improvement in some performance 
tasks, such as sprinting and vertical jump, although the improvements 
are generally small, highlighting the difficulty of distinguishing the effects 

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Copyright © National Academy of Sciences. All rights reserved.
Educating the Student Body: Taking Physical Activity and Physical Education to School
130