Anecdote: I used to work from home and pretty much sat down the whole day. I would still go for a run once or twice a week, but I would quickly experience a sharp pain in my lower back that made it really hard to run. Some Googling led me to believe that my tight hip flexors might be causing my back pain, and that sitting down all day could lead to tight hip flexors. I've since started working for a couple of hours per day at a ghetto standing desk and my back pains are pretty much gone.

Another thing that I really highly recommend is Joe DeFranco's stetching programme, Limber 11 (https://youtu.be/FSSDLDhbacc). You can do the whole thing in about 10 minutes, and it leaves your whole body feeling nice and relaxed.