Why do muscles feel sore one to two days after exercise?

This phenomenon is called delayed onset muscle soreness, or DOMS. It occurs because intense or unfamiliar exercise, especially movements that involve eccentric contractions where muscles lengthen under load, causes microscopic tears in muscle fibers. This mechanical damage triggers an inflammatory response as the body sends white blood cells and other immune agents to repair the tissue. The soreness peaks at 24 to 48 hours after exercise because the inflammatory process and associated fluid buildup take time to develop. Chemical irritants released during this repair process stimulate pain receptors in the muscle. The soreness typically fades as repair progresses, and the muscle adapts to become stronger and more resistant to similar damage in the future.