Men who spent more than 23 hours a week watching TV and sitting in their cars (as passengers or as drivers) had a 64 percent greater chance of dying from heart disease than those who sat for 11 hours a week or less. What was unexpected was that many of the men who sat long hours and developed heart problems also exercised.

What a counter-intuitive result...you can't sit for hours at a time even if you exercise regularly.

Its hopeless...

Phys Ed: The Men Who Stare at Screens - Well Blog - NYTimes.com