It should perhaps be stated first of all that I'm not the most physically fit individual you will ever meet. I'm really not huge by any means, but I'm frankly I'm happy with myself. With my career path being what it is, it means that I will spend the majority of my time in front of a computer and there are some would use this as an excuse to never do anything other than be at a computer. However, the truth of the matter is that every often you really do need to get up. I'm not saying "Go run a mile" or "Start working on those six pack abs" I mean you can if you want I certainly won't discourage you, but at very least you need to just get up and take a little walk. Skipping over the physical health benefits: stretching your legs, helping prevent cramps, reduce eye strain, etc, it actually does a lot for you mentally.