alexch's almanac

As for the idea that lactic acid causes muscle soreness, Dr. Gladden said, that never made sense.

“Lactic acid will be gone from your muscles within an hour of exercise,” he said. “You get sore one to three days later. The time frame is not consistent, and the mechanisms have not been found.”

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.