Stupid question maybe - just wondering.....

If you've got predominantly fast twitch muscle fibres you probably won't be an elite marathon runner, but you can still train to the peak of your potential and be a decent distance runner. And if you've predominantly got slow twitch, you're never going to challenge Usain Bolt. And there are loads of other factors to consider too.

So the way I'd look at it is this - genetics determines your potential, training determines how much you can tap into that potential, and both will impact your level of achievement.

I was under the impression that there's no interconversion between types of muscle fibre - you're born with your ration of each and that that's. You can train them, but not change between them. I could be wrong

IIRC fast twitch fibres can and do take up the work of slow twitch fibres as and when the slow twitch ones become knackered, and this is part of the rationale for incorporating some speed work (i.e. actual speed work) in marathon training.  So the one way conversion does make sense.  It's probably on p4,365 of Noakes or something.

popsider wrote (see)

Interesting point with natural sprinters training for distance. I know the cyclist track sprinter Dave LeGrys - former elite rider and current masters world champ you can google him - took up marathon running at one point and got down to 2.38 as a veteran - so nothing like elite but not too shabby given he wasn't a full time athlete and didn't have a background in distance running. I had a short discussion with him once via pm from a forum thread elsewhere and he reckoned that natural sprinters could have more success converting to distance athletes than vice versa - something to do with fast twitch fibres converting to slow twitch better but not the other way round.

But a top marathon runner could do 100m in 11 seconds, which is14% slower than the world record, 2:38 on the other hand, is some 22% slower than the marathon world record...

Bubblegum Boots wrote (see)

But a top marathon runner could do 100m in 11 seconds

Pull the other one!

Here are some informative articles about the impact of training v genetics.

Part 1

Part 2

Part 3

Hopefully also helping disproving the bollocks written by a couple of recent authors on the topic.

Every school has about 5 boys that run faster than 11 seconds when timed by their teachers on unmeasured grass tracks.  Unfortunately in the real world sub 11 takes a lot of speed - more speed than the vast majority of top marathoners would have.

dibbers - just joking, no problem.

Spoons. wrote (see)

 So going back to my original point, if someone starts training at, say, age 40, doesn't have any background in running or exercise, and doesn't have the perfect genetics, how good could they be with the perfect training. I guess they could never actually train as hard as the elites as they would just get injured. Would a sub 3 hour marathon be in range for anybody who put the hours in?

I think if you have the correct mental attitude, life doesn't get in the way, you stay relatively uninjured, and you have the correct coaching then anything is possible. 

Because everyone is different its impossible to predict what will be achieved but with all the correct measures in place you can get yourself in the best position to achieve great things.  Though maybe not the Olympics.