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