I have heard that the amount of Fast twitch muscle fiber a person is born with is the determining factor on how fast a person can run or the height of their jump and they are born with a certain amount and nothing can be done to change it. Is this true?
I’d like to know that also. And as an extension of that question, how can you determine this in children, say, 6-10?
Muscle fibers are plastic to some extent. So called transitional fibers can be influenced to take on fast or slow characteristics based on training. I have also heard that fibers are not really the limiting factor, it is the nervous system. That is, if you hook a slow twitch fiber up to a fast twitch neuron, it will take on fast twitch characteristics (and vise versa.)
Some common tests for fast twitch potential in children are the standing vertical jump and standing long jump, but these are imperfect at best. Basically, my advise is don’t worry about fiber composition. Train right and strive to reach your own genetic potential…few even make it that far.
I agree with xlr8. 
Agreed. Why worry about the things you cannot control?
Agreed2. Why worry. Just try to train correctly right now. Anything that was done before is in the past. Every once in a while I wonder if I’ve done irreversible damage to my potential in the years I was inactive … I always reach the same conclusion though - it’s a waste of time to worry, it’s much more useful to worry about reaching what I can now. I think it applies to all stages of development though.
Well the reason I asked is because what if you had a little brother or sister or something and wanted to know what they would be better suited for, sprinting or distance. What methods can you use to determine this?
If my memory serves me correctly, the soviets did a fine job of this by mandating a ton of correct physical development very early on (i.e. ages 6-10) and then evaluated a little later… From what I understand (i’ve only read a few articles on elitefts about this) actual specialization didn’t occur in the soviet system until 17-18… In general all of there athletes had the same prepatory background, until such time specialzation was neccesary. — far better in my opinion is to avoid specialization or very rigourous training until later (HS at the absolute earliest). Re: always wondering what my potential could’ve been - yeah, I think we all do that, especially after that first bit of success.
I understand exactly what you mean. But what if they join a track club. They have to do some kind of practice. you cant run them in really fast stuff and put them in a distance event. Does that make sense?
DaGovernor,
i would ask the little brother or sister what they enjoy more. people tend to move towards what they are good at.
Once again I understand. Maybe I am over thinking this but, what if they have no preference? Do you just throwm in anything, and let natural progression and fate take him/her to the event they end up being good at (meaning move them up or down in distance as needed)?
If they have no particular preference to an event, why not have them trying out different events through out a number of competitions. ie. first competition, one throwing event, a sprint event and a jumping event. Eventually they will find an event that they prefer over the others. Lots of people get lost in trying to find what event a child is best suited, in my opinion there best suited for the event they enjoy the most, it’s suppose to be about fun at this stage in the game.