Objectively:
http://www.gaitposture.com/article/S0966-6362(09)00602-X/abstract
With TV and other non-sedentary SB:
http://onlinelibrary.wiley.com/doi/10.1111/j.1467-789X.2008.00508.x/full
In Epidemiology:
http://www.sciencedirect.com/science/article/pii/S0749379711003138
http://www.ncbi.nlm.nih.gov/pubmed/23045206
If you would rather not read through these papers, have a look back to my blog on the 10th July to view my overview of measurement of sedentary behaviour.