Many of us sit all day at a desk and so we don't get much exercise. If you're looking at a computer screen, you should look away every so often to rest your eyes. You should also get up from your chair every so often to stretch your legs.
You can even take a few minutes several times a day for a mini-retreat from the stress -- right at your desk. Try some stretching exercises for your arms, back, legs, and neck. Another idea is to practice progressive muscle relaxation.