Lactic Acid Is Your New Best Friend

Jane Brody sets the record straight on lactic acid: Long believed to be a caustic waste product, lactic acid is a good thing, says Brody–it’s the fuel the muscles make from glucose and burn for energy.  Brody tells us that the reason trained athletes can perform so hard and so long is
because their intense training causes their muscles to adapt so they
more readily and efficiently absorb lactic acid. They can do that, says Brody, because training can double the mass of our mitochondria, which she describes as "the energy factories inside out muscles."
The Times quotes George A. Brooks,  a professor in the department of integrative biology at the University of California, Berkeley, who tells us why, just before a race, coaches often tell athletes to train very hard in brief spurts. That extra stress increases the mitochondria mass even more, says Brooks, and that extra mass can boost performance.
Read more about lactic acid at Time-to-Run.