Sitting has become one of the things we do most in the day. Wake up, sit for breakfast, drive in the car to work to then sit in your office for hours upon end, to then go to lunch, dinner then lay down for sleep. Excessive sitting is linked to negative metabolic and cardiovascular effects. It can also weaken and tighten muscles in our lower region.

Let’s begin with some anatomy. Our hip region is the prime mover for power and locomotion. Sitting places our hip flexors in a shortened/tightened position while our hip extensors are being lengthened or weakened. If we stay immobile, and do nothing to counter the negative effects, physical health and ability can be detrimentally impacted.  A simple squat self assessment can be used to evaluate the effects of prolonged sitting – if you are unable to squat with a full range of motion with good form or unable to do so without discomfort then implementing some of these stretches and exercises can help. 
Stretches for tight hip flexors: couch stretch, long lunge
Glute strength: glute bridges, squats
Thoracic spine: balance pushing and pulling movements (bench, push ups, rows etc.)
Standing workstations:
Many companies are starting to shift to standing work desks. This can be a great way to break up all of the sitting in your day. If you cannot have a standing work station, try to position your computer monitor facing slightly higher than eye level helping keep head tilted up and body in a good position. When we sit at a computer our shoulders tend to slump, resulting in protracted scapulae and unstable shoulder joints and tight pecs in addition to the lower body issues that arise.
Use the 55:5 rule. For every 55 minutes on the hour, take 5 minute to get up, walk around the office, maybe do some squats, stretches, check in on your water intake.  A timer on your watch or phone can serve as a great reminder tool for you to get up and get moving.  There are also apps like TimeOut that can be useful in ensuring you take a break!  During your 5 minute break walk around the office, go up a flight of stairs, march in place  – just do something other than sit.
Build at least 30 minutes of moderate activity a day (re: brisk walk) – this can be broken up into 5 minute bouts throughout the day – ie. employing the 55:5 rule 6 times throughout the day.  Keep in mind, this is not an exercise recommendation as that is something entirely different; this is a suggestion for staving off the negative effects of prolonged sitting.
In terms of position, try to sit tall with your bum behind you. Rolling your shoulder up and back then down with a relaxed upright torso.  Keeping your posture in check will also help reduce tension in the neck and shoulders that is commonly felt after a day at the office.