Bloggers, too much sitting can offset the benefits of regular exercise

Participation in sport is associated with a with a 20—40% reduction in all-cause mortality compared with non-participation. Exercise might also be considered as a fifth vital sign, according to the Lancet: http://goo.gl/gyxYf

From the NYTimes:

Wrong: Sitting at your cubicle. Better: Walking while clicking and talking.

Your chair is your enemy.

It doesn’t matter if you go running every morning, or you’re a regular at the gym. If you spend most of the rest of the day sitting — in your car, your office chair, on your sofa at home — you are putting yourself at increased risk of obesity, diabetes, heart disease, a variety of cancers and an early death.

In other words, irrespective of whether you exercise vigorously, sitting for long periods is bad for you.

"Health Promotion" video: Benefits of exercise.

References:

Stand Up While You Read This! - Opinionator Blog - NYTimes.com
How to Exercise WHILE Blogging or Doing Other Computer Work