First it was fat. The all-purpose dietary demon has been mostly rehabilitated into an important part of a healthy diet.

Now it's lactic acid. When I first started lifting in commercial gyms, in the early '80s, the accepted wisdom was that lactic acid caused post-workout muscle soreness.

Not only has that one been debunked, but new research from Australia and Denmark shows that lactic acid actually helps a muscle perform better. From The New York Times:

"After a muscle fiber has worked intensely for a while, it begins to lose potassium, and that dampens the fiber's ability to contract. Lactic acid, by blocking the movement of chloride across the fiber's surface membrane, helps the muscle fiber recover its ability to work, said D. Thomas Pedersen, a doctoral student at the University of Aarhus who co-authored the study.

"The fatigue an athlete feels is likely caused by the loss of potassium rather than the build-up of lactic acid, Mr. Pedersen said.

"The finding may explain why some 100-meter runners find it beneficial to sprint a short distance 10 to 15 minutes before a race. 'You build up a little bit of lactic acid to prepare your muscles for the coming exertion,' Mr. Pedersen said."

Tags: strength