If you spend 80% of your day sitting down, standing up becomes a huge extreme for the subconscious. All of a sudden, standing up will have a huge chemical cost and to avoid this cost, you will try to find much more efficient ways of moving around. Generally, this means adopting a morphed version of a seated posture whilst walking and running.
POSTURE is the hierarchy of correct standing, walking and running. The two key elements of this are thoracic extension and hip extension.
Here are the TEN prep exercises we recommend for Good Running Form.