Some research has been conducted to identify Lactic Acid as a fuel. This is good for your muscles to use when exercising. But many believe it is bad to reach your lactic acid threshold and the sign of pain or soreness is an indication to stop. Though lactic acid has no correlation with muscle soreness at all. muscle soreness is caused by tears in the muscle. Many on the other-hand speculate that lactic acid is bad for you and some believe it's good? what are your thoughts about what lactic acid (good or bad) and the reason behind it building up during exercise?