Long periods of remaining in one position during waking hours is inherently an unnatural physical stress to place on our bodies. According to Safe Work Australia sedentary work is an emergent occupational health and safety issue that is “linked with an increased risk of premature mortality, chronic health disorders and detrimental work outcomes.”

Due to the static nature of office-based work, general neck and shoulder tightness, with reduced mobility of the spinal joints, is commonplace. Administrative and office workers are at increased risk of musculoskeletal injuries associated with prolonged sitting. Sedentary work also affects non-office blue-collar workers across many occupations such as truck drivers, delivery drivers and machine operators.
Active offsets to sedentary work include:
Take regular ‘mini breaks’ from the computer desk Regular mini breaks help increase circulation, limit fatigue and encourage mobility.
Encourage ‘Walking Meetings’ or ‘Standing Meetings’. Next time you have a meeting, suggest going for a walk with your colleague. This not only gets you moving, it can also help increase productivity after the meeting. 
Alternatively, stand meetings will offer a nice break from your desk.
Alternate between sitting and standing desk set up. Consider a sit-stand desk. Alternating between standing and sitting allows your body to activate different muscles and rest others, helping to reduce fatigue and limit poor postural habits
At a minimum, try changing your position every 30 – 60 minutes.
Create a group stretch/exercise class at work
Create a daily morning and afternoon stretching/exercise rhythm 
Forget emailing your colleague across the room. You’ll be surprised how much small incidental movements will help revitalise you once you return to your desk, not to mention the improved relationship with your colleagues.
Drink plenty of water. Not only will you improve your health by staying hydrated, but you will be forced to take breaks from your desk when ‘nature calls’.
If possible, when on the phone take the opportunity to pace around the office.