Muscle Fibers, Fast-Twitch

**Definition:** Skeletal muscle fibers characterized by their expression of the Type II MYOSIN HEAVY CHAIN isoforms which have high ATPase activity and effect several other functional properties - shortening velocity, power output, rate of tension redevelopment. Several fast types have been identified.

**Tree numbers:** - A10.690.552.500.500.600 - A11.620.249.400

**Synonyms:** - Muscle Fibers, Type II