There are many causes of sore muscles. Lactic acid buildup was thought to be the main cause of sore muscles after exercises, but that is a myth that has now been discarded. Before we go on to discuss what really causes sore muscles, let us see what this phenomenon is all about. What is Lactic Acid Buildup? Whenever we do something that requires a high amount of glucose to be consumed by our muscles, such as exercise, the energy is obtained from anaerobic metabolism of glucose. The by-product of this is lactate. When we exercise, the amount of lactate produced exceeds the rate at which the muscles can remove it. Hence, it begins to get concentrated in the muscle. This is a very real phenomenon, and is the reason why it was thought to be the cause behind acidosis and sore muscles. Lactic acid, however, merely leads to an uncomfortable, burning sensation in the muscles, especially those of the arms and legs, and is not responsible for the muscle soreness experienced by the person the day after. In fact, the burning sensation is just a warning sign that we are doing something that is a bit too hot to handle for our muscles. What Actually Causes Muscle Soreness? The pain in overworked muscles actually occurs due to microscopic tears that occur in the muscle fibers. When we work out, intentionally or in an unintentional, emergency situation, our muscles are broken down, and are strengthened when they are rebuilt. This process takes a few days, and contains an inevitable phase where the broken muscle fibers are 'noticed' by the brain, which notifies us about it through soreness. If you are working out correctly, the soreness usually disappears within a day, leaving you ready for a fresh, harder workout. How to Ease Sore Muscles? Though stretching after a workout helps clear out lactic acid pent up in the muscles, it doesn't actually help in easing soreness, though it does ease the burning sensation. What does the trick is a proper, protein-rich diet, which replenishes and strengthens muscles effectively. Another trick that helps in post-workout recovery is a cold water bath, which enhances blood circulation, increasing the amount of nutrients being sent towards the broken muscles.