By altering posture. People who worry or stress tend to have altered body posture and causes strain - esp worry and stress cause muscle tension and lead to chronic neck pain, which is often burning in quality. People who worry also tend to keep their body rigid while driving with a tendency to whiplash injuries. It depends on body posture and not being loose and relaxed with flow of movements in body uninterrupted.
Muscle injury. Stress can effect any part of of the body but I have not heard of it causing muscle spasm. I believe if muscles are tight enough from stress it can send them into spasm.