Muscle soreness after exercise, commonly known as Delayed Onset Muscle Soreness (DOMS), can arise from several factors. The primary cause is the micro-tears in muscle fibers that occur during resistance training or unfamiliar physical activity. This soreness usually peaks 24-72 hours post-exercise due to muscle inflammation and the body's recovery process. Factors like exercise intensity, duration, and an individual's fitness level can also contribute. Ensuring proper warm-up, cool-down, and stretching can help minimize soreness, while adequate nutrition and rest facilitate muscle recovery.