Sitting while watching a TV or working at your computer for more than 4 hours a day is a health hazard even if you exercise. Even if you exercise.
Sit less. Get up and move more often. Consider creating your own computer workstation at enables you to work while standing.
From the Conditioning Research blog:
While health officials have issued guidelines recommending minimum amounts of physical activity, they haven’t suggested people try to limit how much time they spend in a seated position.
“After four hours of sitting, the body starts to send harmful signals,” Ekblom-Bak said. She explained that genes regulating the amount of glucose and fat in the body start to shut down.
Even for people who exercise, spending long stretches of time sitting at a desk is still harmful. Tim Armstrong, a physical activity expert at the World Health Organization, said people who exercise every day — but still spend a lot of time sitting — might get more benefit if that exercise were spread across the day, rather than in a single bout.
And a little video on the topic: