The primary cause of post-exercise soreness, known as delayed onset muscle soreness (DOMS), results from microscopic damage to muscle fibers during intense or unfamiliar physical activity. This damage triggers an inflammatory response, leading to pain and stiffness, typically peaking 24 to 72 hours after exercise. While preventing DOMS entirely is difficult, gradual progression in training intensity, proper warm-ups, and cooldowns, along with adequate recovery practices, can help minimize its severity.