There is magic to be had for your body by just doing some movements throughout the day instead of simply sitting at your desk! Move around! Motion is the potion that will help you feel better!
Core focused motion!
Moving does more for your body tone than anything else! Doing simple little exercises at your desk while working or getting up the correct way will help you to strengthen your core as well as burn calories without putting forth a huge effort. Turn your day in the office to an exercise plan that will make a big difference in how you feel. The stairs are your friend, use them instead of the elevator.
Pretend the bench is your chair, no dumbbells in your hands
When sitting at your desk, sit at the front of the chair, do not "sink" into the chair. Pull your core tight, pulling your belly button to the back of your spine. Feet together. Keep your shoulders straight and back, the spine should be flat, especially keeping your core tight that forces the lower back to be flat instead of curved in(Check example above). Remember to breath while doing this. When you have your core position correct, flex your glutes, making them as tight as you can and hold it for a couple of seconds then release for a second and tighten again, repeat this over and over. You should begin to feel a burn, this is a workout without a lot of work, while at work!
If you have a hard time getting the position on your chair correct, imagine you are sitting on a balance ball.