Skeletal Muscle: The Difference Between the 3 Fiber Types

Skeletal muscle fibers can be broken down into three types. Type I (slow twitch), type IIa (fast twitch intermediate), and type IIx (fast twitch). Type I contract and relax slowly while producing low amounts of force. Type IIa contract and relax fast while producing high amounts of force. Finally type IIx contract and relax the fastest while being able to produce the highest amount of force. Type I fibers fatigue the slowest while type IIx fatigue the fastest.

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