According to Fitness.gov:
This lack of activity doesn’t just affect your health; it can have a direct impact on your work performance and employee engagement. According to studies in the American College of Sports Medicine and published in the Journal of Workplace Health Management:
Clearly exercise is beneficial in so many aspects of our lives, even in our jobs (don't forget that sitting for prolonged hours is actually harmful to your health). But not all of our workplaces sponsor lunchtime yoga or have gyms on site. Even then, it’s difficult to find the time. However, there are eight exercises you can do right at your desk — some even while you’re sitting down.
You can do these leg and abdominal exercises even when you’re in a meeting or on a conference call without people noticing. Sit upright in your office chair. Straighten your left leg so that it is parallel to the floor and hold it in place for 10 seconds. Now, do the same thing with your right leg. Repeat both legs for 15 repetitions. One you build up strength, try adding weight to your legs by looping your purse or briefcase on your legs while you do the raises.
A variant of the above exercise works out your core. Just like above, sit upright in your chair. But this time, raise both legs so that they are parallel to the floor. Slowly lower your legs until they are hovering an inch or two above the ground. Hold the position for as long as you can, and then release.
Sit in your desk chair with your feet flat on the ground. Rapidly tap your feet in place, just like you would do if you were running in place. Do this for 30 seconds. Pause. Then do it for another 30 seconds. Work this in every half hour or so to bring up your heart rate without breaking a sweat that will embarrass you at your afternoon meeting.
For this exercise, you need an office chair that won’t roll away from you. Scoot up to the very front edge of your chair, place your legs out in front of you, and place your hands on either side of your hips, fingers pointing toward your desk. Grasp the edges of the chair with both hands, and use your core and arms to raise your body up off the chair and then down so that your rear goes down toward the floor. Push yourself back up, and repeat 15 times. Do three cycles of 15.
Not only will this exercise raise your heart rate and bring in some cardio, but it will also be a good stress release if you had a particularly frustrating day at the office. Raise your fists up in front of your face in a boxing position — while you’re sitting a safe distance away from your computer. Punch your fists forward in the air, as if you are using a punching bag, switching back and forth from right arm to left. Do this for 30 seconds. Pause. Repeat for 30 seconds. Again, like other cardio exercises, work this repetition into scheduled intervals in your work day.
For a simple, effective variant on your favorite free weight exercises, take two filled water bottles. Using these as weights, do overhead presses, arm curls, and other simple gym-style workouts right at your desk.
Remember when you were a kid and there was nothing better than a desk chair that spins? Use that fun as a grown-up for a great ab workout. Sit upright in your swivel chair and lift your feet off the ground. Lightly hold on to the desk with your fingers — but ensure that your hands or arms aren’t doing the work here, because it should be all core oblique abdominals here. Use those abs and the rest of your core to swivel the chair from left to right and back again. Do 15 repetitions in three cycles.
This exercise requires you do get up from your desk chair, but it can be great while you’re waiting in line for the coffee machine or the microwave, or in those few minutes when everyone has left the conference room after a meeting. This is a variant on a plank exercise, using a very similar form. Step back so that you are at least a foot away from a wall and then lean forward against it using only your forearms for support. Hold this position as long as you can.
For a variant, get into the leaning position and lower yourself until your shoulders almost touch the wall, too, and push yourself back up. Repeat 15 times.