According to a recent article over at Ergoweb, obesity can be a factor in workplace injuries such as MSD (musculoskeletal disorders) and RSI (repetitive stress injuries) because “the workplace is an ill-fitting environment for the obese. Standard chairs and workspaces are too small, and the mismatch can trigger musculoskeletal disorders (MSDs) and reduce productivity.”
You can find the article here: Ergonomics Finds a Growing Role in Reducing the Cost of Obesity for Employers . It discusses some of the steps ergonomists are taking (workstations with adjustability features–and teaching employees how to use them properly–seem to be key). The article also has links to other reports on the topic.