What are good exercises for folks who spend much of their day sitting at a computer?

The answer is simple. Get up and move around frequently during the day. While you could do calisthenics in your cubicle or standing desk pushups, your co-workers may not appreciate your workout.

Office Exercise

If you have trouble staying fit at work, these office exercises are a great way to keep your body moving right at your desk. The moves here involving stretching and strengthening your body, all within the comfort of your office chair. This workout doesn't take the place of traditional strength training, but offers you a way to keep your blood moving if you can't get away from your desk.
Precautions
See your doctor before trying this workout if you have any injuries, illnesses or other conditions. Make sure the chair you use is stable.  If you have wheels, push it against a wall to make sure it won't roll away.
Equipment Needed
A chair and a water bottle or light-medium dumbbell.

Click on the pictures for closer look
Stretches for Your Wrists and ArmsWrist Stretch: Extend arm in front, palm up and grab the fingers with other hand. Gently pull the fingers towards you to stretch the forearm, holding for 20-30 seconds. Repeat on the other side. Wrist & Forearm: Press hands together in front of chest, elbows bent and parallel to the floor. Gently bend wrists to the right and left for 10 reps. Lower Back Stretch: Sit tall and place the left arm behind left hip. Gently twist to the left, using the right hand to deepen the stretch, holding for 20-30 seconds.  Repeat on the other side.
Lower Body Exercises Hip Flexion: Sit tall with the abs in and lift the left foot off the floor a few inches, knee bent. Hold for 2 seconds, lower and repeat for 16 reps.  Repeat on the other side. Leg Extension: Sit tall with the abs in and extend the left leg until it's level with hip, squeezing the quadriceps. Hold for 2 seconds, lower and repeat for 16 reps.  Repeat on the other side. Inner Thigh: Place towel, firm water bottle or an empty coffee cup between the knees as you sit up tall with the abs in.  Squeeze the bottle or cup, release halfway and squeeze again, completing 16 reps of slow pulses.
Chair Exercises Chair Squat: While sitting, lift up until your hips are just hovering over the chair, arms out for balance.  Hold for 2-3 seconds, stand all the way up and repeat for 16 reps. Dips: Make sure chair is stable and place hands next to hips. Move hips in front of chair and bend the elbows, lowering the body until the elbows are at 90 degrees. Push back up and repeat for 16 reps. One-Leg Squat:  Make sure the chair is stable and take one foot slightly in front of the other.  Use the hands for leverage as you push up into a one-legged squat, hovering just over the chair and keeping the other leg on the floor for balance.  Lower and repeat, only coming a few inches off the chair for 12 reps.  Repeat on the other side.
Upper Body Exercises Front Raise to Triceps Press: Sit tall with the abs in and hold a full water bottle in the left hand.  Lift the bottle up to shoulder level, pause, and then continue lifting all the way up over the head.  When the arm is next to the ear, bend the elbow, taking the water bottle behind you and contracting the triceps.  Straighten the arm and lower down, repeating for 12 reps on each arm. Bicep Curl: Hold water bottle in right hand and, with abs in and spine straight, curl bottle towards shoulder for 16 reps. Repeat other side.
Ab Exercises Side Bends: Hold a water bottle with both hands and stretch it up over the head, arms straight. Gentley bend towards the left as far as you can, contracting the abs. Come back to center and repeat to the right. Complete 10 reps (bending to the right and left is one rep). Ab Twists: Hold the water bottle at chest level and, keeping the knees and hips forward, gently twist to the left as far as you comfortably can, feeling the abs contract. Twist back to center and move to the left for a total of 10 reps. Don't force it or you may end up with a back injury.

Jack Dennerlein, a professor at Northeastern’s Bouvé College of Health Sciences in Boston who specializes in ergonomics and safety, suggests a variation on the 20-20-20 rule used to reduce eyestrain. In the case of the eyes, the rule is to take 20 seconds to look at something 20 feet away (instead of your computer), and repeat this every 20 minutes. But Dr. Dennerlein notes that this eye rule can be applied to movement as well. Every 20 minutes, walk 20 feet away for 20 seconds or more. Stop by a co-worker’s desk. Get a cup of coffee. Pace. Just don’t sit.

An interesting solution for both sore backs and a sedentary workday is the sit-stand workstation. (For more information about these stations, you can read the article “Taking a Stand for Office Ergonomics.”) Dr. Dennerlein said he now has one both at the office and at home and likes the effect it’s had on his work habits.

“It gets me moving around,” he said. “It keeps me varying my postures. When I stand at my desk, if I’ve got a thought I’ll walk around. Instead of just sitting and turning and looking at the window, if I’m already standing then I’ll walk over to the window and come back.”

Dr. Dennerlein notes that standing for long periods of time is not good for you either. The key is to vary your work posture throughout the day. “Just keep moving and changing things around,” he said. “I think people should be empowered to make adjustments to see what feels right for them. And one thing that might feel comfortable in the morning might not feel comfortable in the afternoon.”