Sitting too much is not the same as too little exercise.

Intense exercise for an hour a day will not fix the metabolic changes caused by sitting all day!
To be more exact, "the deep red quadriceps that are designed for postural support...quickly lost more than 75% of their ability to siphon off the fat circulating in the lipoproteins from the bloodstream when incidental contractile activity was reduced" and in the poor exercise-deprived rats had "a profound decrease in the concentration of plasma HDL cholesterol (22%) on the first day of inactivity."
So we don't need to burn ourselves out at the gym...just keep moving, and get up off our chair every hour. 
You can read the entire manuscript here by author Neville Owen PhD  from The University of Queensland, Australia, who fervently believes that this is a serious public health issue.