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Educating the Student Body
period of “adiposity rebound” (the increase in BMI in midchildhood fol-
lowing the decline in early childhood) and puberty are times of risk for 
excess fat gain that correlates with future adiposity (Rolland-Cachera et al., 
1984). Physical activity and BMI are inversely correlated in children and 
adolescents, although the correlations are modest (Lohman et al., 2006), 
reflecting the difficulty of measuring physical activity, as well as variation in 
body composition and physical activity at a given weight (Rowlands et al., 
2000). Indeed, when studied separately, fat mass index (FMI, or fat mass 
divided by height squared) and fat-free mass index (FFMI, or fat-free 
mass divided by height squared) are both inversely related to physical activ-
ity. With FMI controlled, however, FFMI is positively related to physical 
activity, indicating that, for a given level of body fat, individuals with more 
fat-free mass are more active (Lohman et al., 2006). BMI cut-points for 
defining overweight and obesity have historically been based on age- and 
gender-specific population distributions of BMI. Recent work has shown 
good correspondence between BMI standards and percent fat standards 
that are referenced to health criteria (Laurson et al., 2011). These new 
standards should prove useful for identifying children and adolescents at 
risk for higher levels of cardiometabolic risk factors.
Percent body fat Direct measures of body fat as a percent of weight 
provide a better index of adiposity and health risk than BMI (Zeng et al., 
2012), which is confounded by variation in lean tissue mass relative to 
height. Recently, percent fat growth curves were established for representa-
tive samples of U.S. boys and girls using National Health and Nutrition 
Examination Survey (NHANES) data (Laurson et al., 2011; Ogden and 
Flegal, 2011). Median percent fat for boys aged 5-18 ranged from 14 to 
19 percent and for girls across the same ages 15 to 28 percent. In both 
boys and girls, percent fat increases slowly during early childhood, with 
girls having a consistently greater relative fatness than boys after ages 5-6. 
In girls, percent fat increases gradually throughout adolescence in the same 
manner as fat mass. In boys, percent fat increases gradually until the adoles-
cent growth spurt and thereafter gradually declines until about age 16-17, 
reflecting the rapid growth in fat-free mass relative to fat mass. After 
age 17, percent fat in males gradually increases again into adulthood. 
The increased prevalence of child and adolescent obesity as defined by 
BMI presumably also reflects increased adiposity, although the degree is 
not certain as population-based estimates of percent fat have only recently 
been developed (Laurson et al., 2011). Health-related percent fat standards 
recently were developed by determining levels of body fat associated with 
greater occurrence of chronic disease risk factors defined by metabolic syn-
drome (Going et al., 2011). In boys and girls aged 12-18, body fat above 

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Educating the Student Body: Taking Physical Activity and Physical Education to School
Relationship to Growth, Development, and Health
 
125
20-24 percent and above 27-31 percent, respectively, was predictive of 
metabolic syndrome.
Physical activity is inversely correlated with percent body fat (Rowlands 
et al., 2000; Lohman et al., 2006), although the correlations are modest, 
and changes in overall fatness as well as subcutaneous adipose tissue with 
habitual physical activity are reasonably well documented in children and 
adolescents (Gutin and Humphries, 1998; Gutin and Owens, 1999; Dionne 
et al., 2000). In youth, as in adults, the effects of exercise without caloric 
restriction are modest and are influenced by the initial level of body fat and 
the duration and regimen of exercise (Going, 1999). Experimental studies 
have documented reductions in percent body fat with aerobic exercise, 
especially in children and adolescents who are overweight or obese at the 
initiation of an exercise program (Davis et al., 2012). Regular physical 
activity also affects adipose tissue metabolism (Gutin and Owens, 1999). 
Individuals who engage in aerobic endurance exercise training have an 
increased ability to mobilize and oxidize fat, which is associated with 
increased levels of lipolysis (Depres and Lamarche, 2000). Similar informa-
tion on adipose tissue metabolism in children and youth is lacking, although 
one can reasonably expect similar adaptations in older adolescents.