Does Lactic Acid Cause Muscle Soreness?

The short answer is no. Lactic acid build up in the muscle does not cause muscle soreness. Delayed onset muscle soreness (DOMS) is caused by micro tears in the muscle fiber during exercise. Over a day or two inflammation and swelling (inside the muscle) occur causing the soreness.

Lactic acid is a byproduct of glycolysis (breakdown of carbs into energy). As you exercise, especially as you increase the intensity throughout the exercise, lactic acid builds up in the muscles. However, the lactic acid is quickly converted back to pyruvic acid and placed back into the system to be used again. Most of the lactic acid build up is removed within minutes and is completely gone after about an hour.

Now you know. Lactic acid does not cause muscle soreness, working hard does.