Muscle soreness as a term is not a clinical diagnosis, but rather a symptom. A sore muscle is a common `side-effect` of a hard exercise session but it also can mask an injury to the muscle. There are some characteristics of a normal muscle soreness including minor-to-moderate severity, not affecting functions of daily living, and improving after 72 hours post-exercise session. 

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If you experience significance soreness that is out-of-proportion to the expected or previously experienced soreness (or that is of severe intensity), your functions are affected, the pain intensity was severe at the time of exercise and ongoing, you may be experiencing a muscle tear or a rare but significant condition called post-exercise rhabdomyolysis. These need immediate assessment by a qualified doctor.