As far as associations are concerned, issues of causality – the importance of which is easily understood when considering childhood obesity and inactivity. Either inertia leads to children gaining weight, or the weight leads children to become inactive have very different effects
My public concern is that obesity in childhood leads to inactivity, and there is evidence to support this claim, including this study, where when seen over time in people aged 8-11, weight gain predicted inertia, while inertia did not provide for weight gain. this study concluded,
"Fat balance is a better prognostic marker for behavioral and sedentary behavior changes than the other way."
As for what happens, if I could imagine, it would be a combination of systematic bullying related to obesity (multiple studies prove that intimidation is associated with decreased physical activity and obesity has been shown to be the number one target of school bullying, not to mention the fact that the awful can make fun of heavier children when exercising clearly), is one of the worst / slower in a team and the driving effort increases are the heaviest children in reduced MVPA (moderate to severe physical activity).
Now I've written blogs before the Coca-Cola funded ISCOLE trial, almost ignoring the possibility that obesity in childhood leads to inertia rather than the opposite, and recently another study from the ISCOLE team did .
(and if you are interested, here is a published discussion of emails between ISCOLE and Coca-Cola researchers that is not surprising that these relationships have the very real potential to influence the shaping of results even if donors not involved in study design)
The study, the common links between daily exercise and sedentary periods and child obesity, published in the International Journal of Obesity, looked at weekly and weekend MVPA and sedentary time in children aged 9-11 in 12 countries and associations with obesity.
Yes, it was found to be correlated.
Although they have a single rejection line by talking about causality,
"It is not known whether lower levels of physical activity are the cause or effect of obesity",
which did not prevent them from writing this as their final line and their conclusion,
"As children have more discretionary time during weekend days than weekdays, children should be encouraged to increase physical activity on weekends, especially a high level of MVPA"
which, although true to health as a whole, when framed in the explicit context of childhood obesity as it is in this work, seems to deny the most likely case that weight simply slows down children.
And honestly, that matters.
It means that one of the most prevalent stereotypes of obesity is that it is a lazy illness, and the repeated use of ISCOLE frames supports this stigmatizing message. It also means that, given at least by the parents I see regularly in my office, inactive children with obesity are regularly (and sometimes even forgiven or intimidated) by their well-meaning parents because they are not active enough to lead them lighter I can only wonder whether this would still be the case if the meat of the discussions on these kinds of documents focused on the obstacles to physical activity created by childhood obesity itself?
I would like to see more research on the various mechanisms by which child obesity can contribute to inertia and more diachronic studies aimed at testing causality rather than writing paper with conclusions that at least confirm bias ignore the many reasons children with obesity are understood to be less likely to be physically active and in this way poor children fail.