Muscles are usually get pain after the exercise that can occur in everyone, especially in a person who is the beginner or eccentric exercise. The first reason is the lack of flexibility after exercise. If we stop heavy exercise suddenly, the muscles will contract rapidly that cause muscle pain. Another reason, the build-up of lactic acid in muscles leads to muscle fatigue after physical training. For instance, the lactic acids that are formed by the metabolism of carbohydrate in the body and accumulate in the muscles affect the muscles fatigue and pain. The last reason is Delayed Onset Muscles Soreness or DOMs. The tiny fibers within a muscle tear out due to using force more commonly. These are the reasons why the muscle pain and fatigue.