[UG]

I've read two books which appear to contadict one another, one states:

The build up of lactic acid causes muscle fatigue. The muscles need to stop working to allow replenished supplies of oxygen to continue the breakdown of lactic acid into water and carbon dioxide.

The other one says:

In a sprint, muscles rapidly use up glucose and accumulate lactic acid. During the recovery the lactic acid is converted back to pyruvic acid and then to glucose. This requires oxygen to generate ATP...

So which one is correct? Carbon dioxide and water or pyruvic acid then glucose? 
Thanks for your help.

[renge ishyo]

It is quite possible that both (!) descriptions are correct.

It probably depends on the amount of lactic acid generated during the exercise. The glycolytic enzymes perform poorly in an acidic environment. If you convert lactate to pyruvic acid you don't solve the problem because you are converting one acid to another acid.  You don't want all that lactic acid just sitting around waiting to be broken down, so as you begin to generate ATP via the breakdown of pyruvate in the citric acid cycle you can immediately spend some of that ATP you get to convert the excess lactic acid lying around back to glucose. The glucose (or fat stores now that you have oxygen) can be rebroken down later to get back the ATP you need, and the problem of the pH change due to the lactic acid buildup will gradually be solved faster and faster as the glycolytic enzymes do their jobs more efficiently. This works because the amount of ATP you get from the breakdown of one pyruvate molecule is much larger than the amount needed to fuel the conversion of many lactic acid molecules back to glucose.

[Yggdrasil]

Both are correct.  Lactic acid can either be converted back into pyruvate in muscle cells or it can be transported to the liver where lactic acid can be converted to glucose.  I'm not quite sure what sittuations favor one pathway over the other, but both sittuations are possible.

[UG]

Okay, thanks for the replies, I'll take your word on it that both are correct