Why is Lactic Acid bad and/or Good? What happens to Lactic Acid when Aerobic Respiration has Taken Place?

-Lactic Acid, if Built up, will become Painful to Deal with. This will make your Muscles Worn Out and be Painful. -However, least you can still Use your Muscles. -And when Aerobic Respiration has Taken Control, the Lactic Acid will be Broken down by Oxygen [Hence why you Breath Heavily after a Violent Exercise]