On: 'The chair is out to kill us'. Studies point to the health risks of sitting

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It is interesting is that an early study on the health impact of activity compared bus drivers and bus conductors, who also differ in sitting/standing:

http://circ.ahajournals.org/content/122/7/743.full#ref-1

Edit: sorry someone else had a better link:

http://www.epi.umn.edu/cvdepi/study.asp?id=13