[surfpel]

> A poor home life in any sense of the term should not matter unless it means the parents are outright abusive

I disagree. Stress from a dysfunctional family or timing demands from being required to act as a caretaker, among other things, will decrease the time and energy required to pursue physical activity.

And physical fitness, high enough to stimulate the indicators they measured, involves more than just causally playing outside - though my interpretation of that sets quite a low bar for the physical exertion involved.