Why does muscle soreness come on late?

Delayed onset muscle soreness (DOMS) typically peaks 24 to 72 hours after exercise, and several factors contribute to this delay:

1. Microtears in Muscle Fibers: Intense physical activity, especially eccentric exercises (lengthening of muscles while under tension), causes small-scale damage or microtears to muscle fibers. These microtears initiate a repair process that strengthens the muscle. However, the tearing itself is not immediately painful. The soreness comes later as the body responds to the damage.
2. Inflammatory Response: After the microtears occur, the body’s immune system sends white blood cells and other inflammatory agents to repair the damaged muscle fibers. This process, which peaks several hours to days after the exercise, leads to the release of substances like prostaglandins and histamines that make nerve endings more sensitive and contribute to the sensation of pain.
3. Accumulation of Byproducts: During the repair process, metabolic byproducts such as lactic acid are generated. While lactic acid itself isn’t the cause of DOMS, the metabolites involved in the breakdown of damaged muscle tissues can cause irritation and contribute to soreness.
4. Swelling and Increased Pressure: In response to muscle damage, fluid may accumulate in the affected area, causing swelling. This extra pressure can stimulate pain receptors in the muscles, leading to soreness. The delay in soreness can be attributed to the time it takes for the inflammation and swelling to develop fully.
5. Nerve Sensitization: Following muscle damage, the repair process also increases the sensitivity of the nerves around the affected muscles. This heightened sensitivity takes time to develop, contributing to the delayed nature of the pain.

In essence, the delay in muscle soreness is due to the time it takes for the body to initiate an inflammatory response, repair muscle tissue, and for the associated byproducts to accumulate and exert pressure on nerve endings.