Physical activity impacts child growth, new study finds
Humans, like all organisms, spend energy (i.e., calories) on a number of critical life tasks, including physical activity. Children must also spend calories in order to grow. When a child's energy supply is limited, metabolic competition for calories can lead to tradeoffs between growth and physical activity; if children are more active, growth should be reduced. While this is logical, there is a dearth of actual documentation for this phenomenon in the scientific literature. As communities in the developing world change their patterns of behavior, it is particularly unclear how these changes are related to increasing body size and body fat.
Taking advantage of a rare dataset spanning twenty years of early economic development in a Maya farming community in Mexico, Dr. Urlacher and his co-author, Dr. Karen Kramer of the University of Utah, analyzed the amount of time that children engaged in nearly 200 different behaviors and used this information to estimate physical activity levels. They show, for perhaps the first time, that children who spend a greater proportion of their overall energy budget on physical activity are significantly shorter, lighter, and have lower levels of body fat than their less active peers. Moreover, they demonstrate that dramatic differences in child body size between 1992 and 2012 (children in 2012 were on average approximately 7 cm taller and 3 kg heavier) are almost completely explained by a reduction in physical activity levels.
This change in physical activity was driven predominantly by less time spent in work and play and more time spent in sedentary activities such as watching television. "This finding has implications for understanding the factors causing the global rise in obesity," said Dr. Urlacher. "More research is needed, but our results suggest that ongoing changes in early life physical activity, in addition to changes in diet, may play a critical role promoting poor metabolic health in the developing world."