Yet, Dr. Brooks said, even though coaches often believed in the myth of the lactic acid threshold, they ended up training athletes in the best way possible to increase their mitochondria. "Coaches have understood things the scientists didn't," he said.

As far as the Sahlin group goes, they ground up muscle tissue, ripped out the mitochondria from cells in the presence of protein-eating enzymes, then looked for a lactate shuttling protein. And low, they didn't find one:roll: Jay, I think that was a good summary, but wouldn't showing that cells can't transport lactate out of them be evidence FOR being able to burn lactate?

First of all, muscle cells can and do transport lactate out of the cell.

Sahlin's group as well as another lab were unable to reproduce Brooks' finding that mitochondria will burn lactate in vitro.

Thus it appears unclear at present, whether [mitochondria] do [burn] in vivo.

Yeah, I think I was getting confused between the transporter and LDH. It was LDH that Sahlin didn't find, right?

Thanks Jay. But it was my understanding that the methods they used were more distructive to the mitochondrial membrane proteins then the methods Brooks employed.

Word.

So, if lactic acidosis isn't responsible for muscle soreness what is?

Jay I'd love to get your thoughts on these claims from the NYT article:

"The understanding now is that muscle cells convert glucose or glycogen to lactic acid. The lactic acid is taken up and used as a fuel by mitochondria, the energy factories in muscle cells.

Mitochondria even have a special transporter protein to move the substance into them, Dr. Brooks found.

Intense training makes a difference, he said, because it can make double the mitochondrial mass."

That, it turns out, increased the mass of their muscle mitochondria, letting them burn more lactic acid and allowing the muscles to work harder and longer."

I've never read anything other than the NYT bit that acted as if it was settled science. Am I worng about this?

First of all "lactic acidosis" is a misnomer. Under anaerobic conditions lactate and acid each accumulate in the cell. The distinction is not trivial or semantic because the "extra" step in glycolysis in which lactate is produced from pyruvate under anaerobic conditions actually reduces the H+ concentration in the cell. Thus production of lactate is thus alkalyzing, not acidifying.


Jay

One point for the sake of semantics-- "Lactic acidosis" is a broader term that refers to the pH state of the extracellular compartment (ie blood) of the body. Under anaerobic conditions in the muscle, where there is production of large quantities of lactic acid, lactic acid is transported from muscle cells to the liver via the bloodstream. In the liver, it is used to produce additional glucose molecules and eliminate lactate (this is known as the Cori Cycle, although it would appear that the study under discussion argues that myocytes/RBCs can bypass the Cori Cycle somewhat by processing their own lactate in their mitochondria-- this concept is controversial, the Cori Cycle is well accepted).

When large amounts of lactic acid/lactate are in the blood stream (headed to the liver), the pH of the bloodstream drops, creating a situation refered to as "anion-gap metabolic acidosis." This is lactic acidosis. An example would be someone who has never trained or exercised and decides to put down their Cheetos, get off the couch, and run a marathon. HUGE amounts of lactate are produce and overwhelm the buffering capacity of the system. Severe lactic acidosis can be fatal.

Local lactate accumulation would be a more specific way of describing what happens when you get the muscle burn during a workout, although I've not spent any time looking into whether lactic acid is directly or indirectly related to somatic pain generation, or unrelated to the pain entirely.

Jonathan

Thank you for confusing the subject by restating the century-old misconception that the cell produces lactic acid under anaerobic condittions. It doesn't. It produces acid and lactate in separate steps of glycolysis; and, in fact - since I love repeating myself - the lactate-producing step in glycolysis is alkalyzing.

Jay