Here is a post that I had up before
Lactic Acid...your friend?!?!
Might want to give it a read.
COmbined with other stuff i've read about lactic acid this is the basic message some scientists are sending through. The build up of lactic acid isn't nessecarilly what makes you stop, the build up is a sign of you nearing your limit.
And it would make sense. When you get stronger you'r muscles need to use less energy to perform the same amount of work in ratio. For example, you start being able to benchpress 100 pounds for ten reps, then get strong enough to rep 150 pounds ten times, your energy ratio for using 150 pounds is the same as when you could only do 100 for ten reps.
Personally I never really went with the idea that you could become resistant to lactic acid. And i'm not a scientist with a degree or anything but, how can you become resistant to an acid? The lactic acid isn't weakening, and if anything the muscle is just becoming more highly bundled.