Visit the National Academies Press online and register for

Sedentary behavior
Sedentary behavior also influences mental health. Screen viewing in 
particular and sitting in general are consistently associated with poorer 
mental health (Biddle and Asare, 2011). Children who watch more televi-
sion have higher rates of anxiety, depression, and posttraumatic stress and 
are at higher risk for sleep disturbances and attention problems (Kappos, 
2007). Given the cross-sectional nature of these studies, however, the direc-
tion of these associations cannot be determined. A single longitudinal study 
found that television viewing, but not playing computer games, increased 
the odds of depression after 7-year follow-up (Primack et al., 2009; Biddle 
and Asare, 2011), suggesting that television viewing may contribute to 
depression. Because of design limitations of the available studies, it is 
unclear whether this effect is mediated by physical activity. 
Television viewing also is associated with violence, aggressive behav-
iors, early sexual activity, and substance abuse (Kappos, 2007). These rela-
tionships are likely due to the content of the programming and advertising 
as opposed to the sedentary nature of the activity. Television viewing may 
affect creativity and involvement in community activities as well; however, 
the evidence here is very limited (Kappos, 2007). Studies with experimental 
designs are needed to establish a causal relationship between sedentary 
behavior and mental health outcomes (Kappos, 2007).
Although the available evidence is not definitive, it does suggest that 
sedentary activity and television viewing in particular can increase the risk 
for depression, anxiety, aggression, and other risky behaviors and may also 
affect cognition and creativity (Kappos, 2007), all of which can affect aca-
demic performance. It would therefore appear prudent for schools to reduce 
these sedentary behaviors during school hours and provide programming 
that has been shown to be effective in reducing television viewing outside 
of school (Robinson, 1999; Robinson and Borzekowski, 2006).
Mechanisms
It is not surprising that physical activity improves mental health. 
Both physiological and psychological mechanisms explain the observed 
associations. Physiologically, physical activity is known to increase the 
synaptic transmission of monoamines, an effect similar to that of anti-
depressive drugs. Physical activity also stimulates the release of endorphins 
( endogenous opoids) (Peluso and Guerra de Andrade, 2005), which have 
an inhibitory effect on the central nervous system, creating a sense of calm 
and improved mood (Peluso and Guerra de Andrade, 2005; Ahn and 
Fedewa, 2011). Withdrawal of physical activity may result in irritability, 
restlessness, nervousness, and frustration as a result of a drop in endorphin 

---

Copyright © National Academy of Sciences. All rights reserved.
Educating the Student Body: Taking Physical Activity and Physical Education to School
138