I havent heard that it was used for a fuel, and i think this essay limits evidence to support that. However, I have read other studies that prove that lactic acid indeed is not what causes muscle soreness. These studies showed that L.A. was a buffer to relieve the muscles from a case of acidosis. So, when muscles become sore, lactic acid comes in to help. This OBVIOUSLY shows why people thought lactic acid was behind soreness.
Hope my gouge helps a little.