I was on boxingscene, and someone said that the ratio of slow to fast twitch are set in every person. Is this correct? cuz I heard you can change the ratio of slow to fast twitch muscle fibers through plyometrics, sprinting, and other anaerobic exercises. Could anyone confirm this? Also, could you create fast twitch muscle fibers without gaining muscle mass?

Also is hand speed in correlation with fast twitch muscle fibers? In the same thread on boxing scene, people think that hand speed is natural and "you're born with it" but 'im just wondering if it's in correlation with fast twitch muscle fibers, and you can develop those type IIb (super fast) fibers, then wouldn't that dispell the myth?