Here's a study where they examined the sedentary behavior among elite professional footballers (soccer)
Another good article on why sitting all day might be undoing your time in the gym.
However standing all day isn't the answer either and you will have similar problems if you just stand all day. The key is constant movement and positional changes. I'm a big fan of Katy Bowman's philosophy on movement and her book move your dna.
How do you achieve that when you have to work at a computer for 8 hours a day?
The first thing you need is a timer or reminder system to let you know its time to take a break or move. I use Workrave, it is free and very customizable. Another article on some other options which I have no experience with.
The defaults on Workrave are quite intrusive. I've settled on a micro break every 10 mins and rest break every 30 mins. It seems to be the general consensus that you need to do something every 30 mins to undo the damage from sitting.
For the micro break a little reminder will pop up on the top of your screen.
If you keep working it will just disappear and then reappear based on the postpone time you set. If you want to take the break you have to stop typing and moving the mouse. The screen will then lock for the time that you set, which in my case is 15 seconds. During these micro breaks I will simply do a quick stretch or stand up for a second. I also avert my eyes from the screen and focus on something in the distance to avoid eye strain. Fortunately I have a window in my office, but you could also look across the room or whatever far point is available to you.
Every 30 mins I take a rest break for 1 min 30s. This is where I will do a little more stretching or exercises and I will also often switch to standing or sitting. One of the nice things about Workrave is that it gives you exercises to do while the screen is locked.
So you can just follow along, or do something on your own. Here are some more ideas for things to do from Sitting Solution.
You will get some funny looks from other employees and I've been asked if I was ok when I was in cube land and doing cat cows on the floor.
Here are some of the different sitting/standing positions I use.
A little difficult to see because the half moon foam pad is black but I'm stretching my calf on it in the above pic.
Ultimately I probably take less breaks than this as I often postpone breaks if I'm heads down but just having the reminder there is a good way to keep me honest.
There are some annoyances with Workrave. It tries to figure out if you're working and when you aren't it pauses the timer. This can be somewhat annoying if you're reading a document because it will pause the timer that whole time. You can set it to reading mode which will turn this feature off
but you have to remember to do that after each time you start Workrave or there are some regedit hacks you can do to change the settings. Check out this article and in particular the comments section for how to edit your regedit file. Not recommended if you're not technically inclined.
Aside from the breaks with stretching there are a couple of other things I do. When its nice out I will take the occasional walk but everyday I walk the stairs a couple times a day.
Once in the morning and once in the afternoon. I work on the 2nd floor and the building has 6 floors. So I take my captain of crush grippers and head for the stairs. Walking up 2 steps at a time I alternate hands with the gripper every flight. Once at the top there is a straight bar railing and I do 10-15 straight bar dips.
Not only am I greasing the groove but this will help me with my 2016 fitness goal to do a muscle up as the final movement is a straight bar dip. I then do a little core work on the hand rails, hold this for 15 seconds or so.
Ok my form looks nothing like that but you get the idea, then head back down. On the way down I'll swing down using the hand rails. Just another way to get a different movement in my day. This all only takes about 4 mins and I'll do it when I need to go to the bathroom so any work time lost is absolutely minimal.
Finally 10-15 mins on the ping pong table in the afternoon. This will actually get my heart rate up to around 115.
Other options are to walk while you take any phone calls on your phone. You could try doing a walking work meeting. Park your car further away. Take the stairs over the elevator. Get creative there are plenty of options but the key is to move as much as possible in different ways and not stay in a static position whether that's sitting or standing. Sitting all day and then killing yourself with a 30 min crossfit wod won't make you healthy.