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Educating the Student Body
cal activity that is enjoyable and developmentally appropriate” (Strong 
et al., 2005, p. 736). In 2008 the Physical Activity Guidelines Advisory 
Committee also reviewed the scientific evidence relating to physical activity 
and the health of children and adolescents (PAGAC, 2008). That commit-
tee confirmed the benefits reported by the previous panel. The committee 
also agreed that it is difficult to select a minimal or optimal dose of physi-
cal activity for youth but reaffirmed the recommendation for 60 minutes 
or more per day of vigorous or moderate physical activity. The committee 
further commented that weekly activity should include some vigorous activ-
ity on at least 3 days and some activities to strengthen muscles and bones.
Available information indicates that relatively few youth achieve a daily 
dose of at least 60 minutes of vigorous- or moderate-intensity physical 
activity. Information on the proportion of youth who are vigorously active 
on 3 or more days per week is not available. However, about 10 percent 
of middle and high school students responding to the Youth Risk Behavior 
Survey (YRBS), conducted by the CDC and state health departments, 
self-reported that on no days in the previous week did they spend at least 
60 minutes doing vigorous- or moderate-intensity physical activity, about 
50 percent reported doing so on at least 5 days, and about 30 percent 
ity on the risk for type 2 diabetes, hip fracture, cardiovascular disease, 
coronary heart disease, stroke, depression, dementia, breast cancer, and 
colon cancer are similarly shaped (PAGAC, 2008) but with slightly differ-
ent slopes (Powell et al., 2011); insufficient data are available with which 
to prepare similar dose-response curves for other health outcomes. Risk 
reduction accrues more rapidly for diabetes and hip fracture and less rap-
idly for breast and colon cancer. Risk reduction for cardiovascular disease, 
depression, and dementia appears to be quite similar to the curve for 
all-cause mortality. These differences are not surprising given the wide 
variety of physiologic pathways through which regular physical activ-
ity produces its various health benefits. The shape of the dose-response 
curve and the differences in the slopes of the curves for different health 
outcomes demonstrate the difficulty of identifying a specific dose or even 
a range of doses of vigorous- or moderate-intensity physical activity that 
should be recommended.