I haven't read the full text to see how they parse it out in either the rationale or the analysis, but it might be related to the fact that a lot of studies on

I haven't read the full text to see how they parse it out in either the rationale or the analysis, but it might be related to the fact that a lot of studies on the effects of sitting actually use data about TV watching. This study might have asked about them separately to gauge the correlation between the two, or just to provide a basis for direct comparison to the TV-based studies.