Regarding fast twitch development, from what I’ve read trying to induce a conversion isn’t worth worrying about. If you increase your lean-body mass then you’re going to have hypertrophy of your muscle fibers, and if you are training specific to your sport then odds are you’re going to get the changes you want.
Kelly Baggett:
Yes, you can train IIB fibers to endure more, but they adapt by transforming to IIA. The difference between type IIA and IIB fibers isn’t worth worrying about from a power/tension standpoint. In fact, if you’re only measruing the ability to generate peak force (or maximum strength), fast twitch vs slow twitch ratio doesn’t even matter. Rather, it’s the total cross sectional area of ALL available fibers that correlates with success.
But anyway, when the IIB are recruited they almost immediately transform into IIA. Athletes don’t express IIBs to much of any degree but sedentary people do.
As an athlete, what you really want is a greater proportion of all IIs over type I, since the type IIs do generate more force than type Is in explosive activities.
Someone with more types I’s naturally excels at more enduring activities whereas someone with type IIs doesn’t. The guy with more type IIs can just engage in more endurance activities, which will transform his IIbs into IIAs, and he’ll then have all the benefits of greater type II fiber but with more endurance.
The guy with more type I’s can really only increase his type IIs through hypertrophy. Take someone with a 50/50 ratio of slow to fast muscles in the thigh. Say he has a 20 inch thigh. Get his legs up to 25 inches and that extra 5 inches of muscle will all be type II fiber. So, now his thighs might be 65% FT and 35% slow twitch.
Which I believe is supported by this study- https://www.springerlink.com/content/x843378082314861/