Thank you for the picture Wikipedia

You see that red part? That is where the rhomboids are located. Why do you care? Because one of the main functions of the rhomboids (rhomboid major for you sticklers) is retraction of the shoulder blade, AKA keeping your shoulders from slumping forward like a caveman and/or cave woman. The more we sit (more on that below), the more our rhomboids weaken and the more our shoulders round forward. Look at the majority of people who work at a computer all day long. Or even look at yourself. If your shoulders are slumped forward there is a good chance you have weak rhomboids.
What one thing do we do every day that kills our metabolism, kills our immune system, makes muscles tight and stiff, and eventually kills us earlier than most people?
We sit at the house, we sit in our car on the way to work, we sit at work for 8 hours, get back in the car and sit, go home and sit on the couch for a few hours and do it all over again the next day. It's a big reason we have an epidemic of overweight people with back problems.Too much sitting shortens your hip flexors, short hip flexors cause back pain, back pain sucks. The circle of life.
I saw a study a few years ago this airplane scientist did. He probably had a name and a cooler title than airplane scientist, but I forgot it. Sorry I know you were all wanting to run out and thumb through airplane research.  This guy normally studied the effect of wind on airplanes, but he took his scientific thingies (name, forgot, sorry) and put them on people to study their movement to discover why some people were overweight and some people were not. Do you know what one activity the people who were overweight did more than any other group? Sat. The normal weight people sat a ton less and moved a lot more. Now I'm sure nutrition played a big role as well, but so does moving and standing. You can burn 100 calories just standing for an hour. So cut that sit out!
So here is my challenge to you. 
For the next week do not sit down for more than 15 minutes at a time.
Set a timer, watch the clock, do what you have to do, but get out of your seat every 15 minutes. Now there will be exceptions (orthopedic or circulatory issues, driving or riding in the car, if I'm on a basketball team, etc...) where it is not possible to get up every 15 minutes. Just get to it as soon as possible.
You can walk around, stretch, or anything you like. Just don't sit so much. After awhile you will notice a lot of lower back and neck pain going away, you will feel more energized and less tired, and you will feel better overall.
If you are reading this on a computer, take a second and realize how your body is positioned. Are your shoulders slumped? Lower back rounded? Head pushed forward, putting your neck in an unnatural position? Did you straighten up as you read this?
Humans are not built to sit in a chair for 40 hours a week or 30 hours on a couch per week. It will be hard to remember to get up every 15 minutes, so make it a priority. You don't forget things that are a priority, so make it important to you because it will help you get healthier overall.