Transforming fats into muscles with exercise or the anxiety that muscles might be transformed into fats when you stop doing exercises are two of the most ridiculous fitness myths. These are stupid myths created by people who have no idea of anatomy and physiology. Muscle and fat cells are completely different structures and can never be transformed into each other.
Muscle tissue is a contractible tissue and demands high energy. Skeletal muscles are the muscles connected to the bones by tendons, which contract voluntarily. We use these muscles when we move. Involuntary muscles, on the other hand are the stomach, intestine and cardiac muscles.
Fat tissue is an adipose tissue which stores energy in the form of lipid. Recent studies revealed that it also acts like a hormone organ. Generally it is present under the skin, around internal organs, in yellow bone marrow, and in breast tissue. Excess fat tissue causes diseases.
Considering these we can say that muscles build up by exercise, and this leads increases burning of fats. Shortly, fat cells cannot be transformed into muscle cells.