If you have a job that requires you to spend long periods of time sitting then it is very important to learn proper posture while sitting. The first step is to purchase a chair that is able to adjust. You will want to sit so that your feet are flat on the floor with you knees being slightly lower than your hips to keep your hip flexors from shortening. You will want your arms to be at a 90 degree angle with your shoulders relaxed and the keyboard at the same level. The center of the monitor should be level with your eyes. If you need extra support for your lower back use a lumbar support.As far as your torso is concerned you will want to keep your ribs level with your abdomen. The next step is too imagine your “butt” bone known as the SITS bones as a tree’s roots being sent downward while at the same time lengthening , growing, and expanding upwardly with you torso while keeping your ribs level with your stomach. The object is to push away from the points of pressure. If you learn to sit this way, your posture will improve and your back PAIN will disappear. Try it out and let me know how it works for you. And as always ” Be good to your Body, and your Body will be good to you”.
Check out this link for more info. on workplace ergonomics https://www.osha.gov/SLTC/etools/computerworkstations/positions.html