Sitting at your desk doesn't mean you can't work on toning your mid-section. You can work your belly at work without your boss ever knowing you're doing some strength training on the job. All you need to do is pull your navel to your spine, the most basic Pilates move [1]. Here's how:

• Sit up straight, keeping your back away from the back of your chair.
• Exhale and pull your abs to your spine without curving your back. This will feel a little like a corset. It should feel a little like you are bracing for a punch to the abdomen.
• Focus on your low abs; these you can definitely keep engaged while you breathe.
• Breathe into your back ribs, wherever you have ribs you have lungs. This is a nice stretch for the intercostals, the muscles between the ribs.
• Hold for 30 seconds. Do twice an hour.

Oblique Variation: To challenge your obliques [2] (the abs on the side of the torso) a little more simply tilt your torso slightly to the right and hold that position for 30 seconds. Then, of course, reverse the action by tilting to the left so you can keep even.

Fit's Tip: You can also work your abs when you're waiting at a long traffic light, when stuck in traffic, or heaven forbid, out on a boring date! Try it right now and let me know how it feels.

Source [3]