The Grey Lady has just gotten around to noticing that it is not lactic acid that causes muscle fatigue, contrary to the common shorthand. This is nothing new; coaches and exercise physiologists have known that for a long, long time. As a bonus, not only is the material dated by at least two decades, the NYT's Gina Kolata woefully misrepresents and misinterprets it as well, which I'm sure comes as a complete shock to anyone familiar with the NYT's sterling reputation for honest, balanced reporting.
Kolata attempts to prove two conclusions: (1) that the presence of lactic acid in the muscles has nothing to do with fatigue; and (2) lactic acid is actually good, since muscles can use it for fuel. She fails miserably on both accounts.
Coaches and personal trainers tell athletes and exercisers that they have to learn to work out at just below their "lactic threshold," that point of diminishing returns when lactic acid starts to accumulate. Some athletes even have blood tests to find their personal lactic thresholds.
But that, it turns out, is all wrong.
Actually, it isn't. The presence of lactic acid in the muscles has very much to do with muscle fatigue. Granted, lactice acid isn't the cause of muscle fatigue, but it is so strongly correllated with muscle fatigue as to be the best measure of the proper training pace. We can easily measure lactic acid build-up. It's not the cause -- some scientists hypothesize that the build-up of hydrogen ions or calcium during exercise causes fatigue, but we don't know. What we know for certain is that lactic acid builds up, and we get tired. Lactic acid is simply a convenient, easily measured marker for a process that we really don't know much about.
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.
It is clear that the old lactic acid theory cannot explain what is happening to muscles, Dr. Brooks and others said.
Yes, it can. And it does, at least in a shorthand way.
As for the idea that lactic acid is fuel, it is. It's just not very good fuel. This piece doesn't get at the relative usefulness of lactic acid as fuel v. glucose. I am fairly sure that muscles will burn lactate in the absence of glucose, but muscles are much more efficient when burning glucose. That's why training at the lactate threshold is so useful -- beyond stimulating increase in mitochondria, it teaches the body to operate more efficiently at higher speeds.
Gina Kolata is an ignoramus who needs to stay on the society page and away from all forms of science, which she clearly cannot get her tiny pea-brain around.