Lactic acid isn't the villain it is made out to be (kind of like blaming the fireman for starting the fire because he was at the scene of the crime,) so it has most likely got nothing to do with the sore legs. Your body knows what is best, sore legs = rest. It is telling you that you are overdoing it a bit. Remember that quality training calls for quality rest. Did you know that lactic acid is produced both in you anaerobic AND aerobic muscles? i.e. it is produced at both sub-maximal as well as maximal intensities. The lactic acid makes its way into the blood stream where it is converted to Lactate. This Lactate serves as a substitute for glucose to help fuel the muscles, which helps conserve glucose in endurance events. This same Lactate in the blood then replenishes up to a maximum of half of your glycogen stores after the ride leaving the other >50% to the break down of fats, certain amino acids and carbohydrates that is present in your body from stored fat, muscle catabolism and your food intake in the 30min post-ride window. A cool down after a hard ride/intervals is very important as it aids in this recovery process, think of it as recovery preparation. Point being that lactic acid isn't a source of the pain but more a by-product of the muscles function in order to sustain the continuous efforts you subject it to. -The above is from Phil Maffetone.
