What takes someone out in a marathon? + clarificatoins

[Manwich5]

What causes one in a marathon to pull away from the other mid race?  4:40 mile pace is world record pace.  Can't the best in the world run that aerobically?  But yet some slow down while others pull away from the rest. 

If that is true then what causes them to slow down?  If they run 4:40 pace aerobically they wouldn't be accumulating lactic acid and therefore not be slowing down or feeling any pain. 


//-----------Clarifications------------------------

And how fast someone runs in any middle distance/distance event is dependent on how slow they accumulate lactic acid which is dependent on how high their aerobic threshold is right? 

How well someone clears lactic acid also helps slow lactic acid accumulation during high intensity running?  800, 1500, 3k, 5k, 10k runners  are always accumulating more and more lactic acid then they are cleraing as the race progresses but the rate is slow because of their conditioning.  And what allows them to kick hard after all the lactic acid accumulation from the previous laps with 1 lap to go is the lactic acid buffers they had trained their muscles to deal with right??


Am I right on this?  I have thinking about this so much trying to tie it all together to fully understand it all.

Thanks

[Ryan]

There are many factors in the marathon. Actually, given that marathon pace is usually run somewhat significantly below one's lactate threshold, by mid-race, I'd be somewhat skeptical that one falls behind due to lactate buildup. More likely, simply muscle fatigue, carbohydrate depletion (which might be a factor of not burning fat as fuel as effectively as one's opponent or might be a less efficient form causing one to burn more energy than one's opponent), hydration or electrolyte balance issues.

[Manwich5]

ah, so basically the difference between the gold medalist and silver medalist (assuming it doesn't come down to final 100 meter sprint or final miles of picking up the pace) is carbohydrate depletion or muscle fatigue?

I guess if the runner doesn't experience these issues (hydration, muscle fatigue, carbohydrate depletion......) they would be dropped simply because of a pace pickup going from marathon pace to lactate threshold pace?  Now the lactic acid starts taking out runners.

[Ryan]

Well, it's a little more complex than that. Obviously, if your LT pace is 5:30 per mile, you're not going to have much luck running a marathon at sub-5:00 pace. However, without writing a book, I think a reasonable simplification of the situation would be that muscle fatigue and low glycogen are generally the triggers for not being able to hold the pace. It gets more complicated largely when you try to explain what causes those things.