Why do muscles feel sore 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 triggers an inflammatory response as the body sends white blood cells and fluid to the damaged tissue to begin repairs. The soreness peaks around 24 to 72 hours after exercise rather than immediately because the inflammatory process takes time to develop. Prostaglandins and other chemical signals sensitize pain receptors in the muscle, making them more responsive to pressure and movement. Despite feeling damaging, this process is part of how muscles adapt and grow stronger, and the soreness diminishes as the body repairs and reinforces the affected fibers.