When you hold a certain position for a long period of time, your soft tissue loses its elasticity, just like an elastic band loses its recoil ability if stretched for extended periods. This also happens in your body, namely to the ligaments.

Furthermore, your joints need movement to help lubricate them; keeping active will help prevent you seizing up and pain free.

Dr. McGill has stated that the ideal sitting posture is one that continually changes, thus preventing any single tissue from accumulating too much strain.

I would suggest every 20 minutes you should change your posture, do some postural corrections, get up and take a short walk, unload your spine or perform the brugger relief position described below; if possible a few or all of the above would be ideal.

Frequent short breaks are better than infrequent long breaks. The most important determinant of risk of injury is not the total time spent performing the activity; what is most important, is how long the activity is performed continuously without interruption.