How your body responds to the apparently innocuous everyday demands you place upon it.
The body is skilled at recognising events that regularly repeat, then adjusting itself to ensure these events are undertaken in the most economical way possible. It's genius is quietly working away in the background to ensure your physical self is fit for purpose.
A purpose you may not have been aware you even set.
Unfortunately the agenda of 'you' ('you' being the more cerebral aspects of you) isn't always in tune with that of the body.
Let's look at an example
'You' set a goal...
I want to build a gigantic and complex world on Minecraft
(not a personal goal of mine, but one I'll use for illustrative purposes)
How your body experiences this goal is not....
'Woohoo! let's together build a gigantic and complex world on minecraft'
Instead it's asked to sit down and be quiet and ignored while 'You' build the gigantic and complex world on minecraft. It's not the same thing.
The request 'you' have made of your body is this....
'You' want to be able to sit still for hours at a time and ignore your body by creating a disconnect between your mind and body that's strong enough to numb anything distracting or uncomfortable in your body that could impede your concentration's ability to attain your goal,
Hmmm, I wonder how your body might feel about this request?
Brain responds like this......
....and goes ahead and does whatever it deems more important than movement regardless of body's opinions.
A good simple analogy is one of asking a dog to sit or wait........for hours at a time.
fidget fidget fidget,
....did you say walk?
....did I sense a walk?
I'm sure your eyebrows conveyed walk?,
what? No, No walk?
Or you might have a body that's a bit more like this....
I won't be quiet!
I'm hurting, I'm bored!
PAIN! PAIN! PAIN!
Oi, Oi, Oi, Oi, Oi, Oi, Oi!!!!!!!!!!
Body ends up sitting around waiting for ages until brain finishes the task, or gets tired or bored and needs a rest.
OMG! Is Brain finished!??
It's time to move!!!!
Or for you maybe this is more like....
The longer your body has to wait the sleepier and more disinterested in moving you become.
Silly brain may be finished the task, but by now brain will probably refuse to do anything for body, and will make body be still again while it watches TV or scrolls on Instagram insisting that's it's exhausted and needs a rest.
(Which may be true. Staring at a screen for hours is draining.)
No matter what the task you set yourself your body has no awareness of the goal in the sense that 'you' do. It is just responding to the physical requirements of the goal.
The goal could be anything.
Watch a film, go to work, write a blog post (I've been sitting writing this one for what fees like ages, but I am on a sick day - body sick, brain feels fine, so I've given my brain something to do while my body rests).
Your body responds to all training stimulus no matter where it takes place. Sitting all day at a desk is a form of training.
5 hours of sitting a day, 5 days per week is a lot of training. You are training 25 hours (or more) per week and, like any form of training it will change the shape of your body over time.
The training effect will be shortening you a bit here, tightening you a bit there, loosening you a bit here, lengthening you a bit there, and so on.
You will unconsciously train yourself through repetition and hours invested to a high standard in the act of sitting.
An Olympic level sitter so to speak.
And as with any athlete, you will be susceptible to injury as an result of your training.
When you stand up from your seat your body won't just give all that training up. You are an Olympic level sitter after all, and everyone knows you don't actually have to be running every single moment of the waking day to maintain Olympic level speed or stamina. You just need to train.
It's the training that's key. Stop the regular training and the training effects diminish.
So you stand up and your body's shortened, tightened, loosened and lengthened bits remain as you have trained them to be.
Your alignment is now all out of place and your standing posture is negatively affected. Ouch!
Just as you have trained this in, you can train it out.
Perhaps consider the idea that all bodies need to move no matter what species they are.
Most people that have a dog understand that it's important for the dog's health to ensure it gets regular exercise. They will be a 'responsible dog owner' and do whatever they need to to ensure this requirement is met; adjusting their scheduling, getting up early or paying someone to ensure the exercise takes place. They wouldn't dream of asking their dog to hold a sit pose for hours on end. In fact this might be viewed as cruel.
What if you decided you were a 'responsible human body owner' and gave this kind of attention and view point to the movement needs of your own body?
Just a thought.
Sit less. Move more.