As far as I understand permanent soreness means you have inflammation process (so called myositis, or just musklce inflammation in plain English). Reasons for myositis, as far as I remember, could be a) chronic infection anywhere in the body as immune system attacks body tissues without making a good difference) b) autoimmune conditions with the specific target on musculosceletal system like RA, etc., c) overexertion for some reasons becasue in that case soreness is caused by local inflammatory agent lactic acid, which is a product of muscle operation, and if not delivered promptly out of the muscles, it causes inflammation and pain, so exertion plus bad blood circulation, that is why soreness is often found in leg muscles. Myositis also is know to be a pure reaction for stress, becasue the body forms muscle tension as part of fight or run reaction.Hope that would help.