I can't think of another sport in which total body alignment affects performance the way it does with running.
Did you know that the positioning of your head when you run can actually negatively influence your running efficiency? You may have noticed some people running with their chins jutted out. This is actually a very common form error that can both strain your neck and throw off your body's alignment resulting in stiffness and soreness during and after a run.
A srong neck supports your head and prevents potential overload in the shoulders and all the way down the body. The proper way to hold your head while running is to keep your gaze straight ahead, using your eyes to periodically look down and watch for obstacles. (Trail running obviously requires a little more attention in this regard).
If you find yourself developing a lot of tension in your neck and shoulders while running, try shrugging your shoulders and shaking out your arms. You can also stop, straighten your posture, and lower your left ear to your left shoulder and vice-versa.