Running Doesn't have to hurt your joints!
The photo on the Left is the "AFTER"
The photo on the Right is the "BEFORE"
See the difference?
The runner on the Left (AFTER) has engaged core muscles and a nice forward lean. The chin is tucked and her vision is focused on smooth forward motion.
The runner on the Right (BEFORE: same runner btw!) has the pelvis tipped forward, shoulders back behind the foot on the ground, which requires more effort and joint strain to apply the "brakes" and "gas" essentially at the same time.