Delayed-Onset Muscle Soreness (DOMS)

Delayed-onset muscle soreness is pain and tenderness on palpation and contraction that begins hours after unaccustomed exercise, peaks around one to three days later and resolves within about a week. It follows eccentric work, where muscle lengthens under load, far more than concentric work. The lactic acid explanation is wrong and has been for decades: lactate clears within roughly an hour, long before soreness appears. The current account involves disruption of sarcomeric and cytoskeletal proteins, a subsequent inflammatory response, and sensitisation of group III and IV muscle afferents.

The usual objective marker, serum creatine kinase, is a poor stand-in. It peaks somewhere between one and four days depending on protocol, varies between individuals by an order of magnitude after the same exercise bout, and correlates only weakly with how sore anyone feels. Reliable high and low responders exist within otherwise similar populations.

The property that matters most for interpreting any recovery intervention is the repeated bout effect. A single bout of eccentric exercise confers substantial protection against soreness and creatine kinase release from a similar bout weeks or even months later. The adaptation is real, large and free.

This makes soreness one of the easiest endpoints in physiology to fool yourself with. Someone who takes a supplement, repeats a workout and hurts less has produced exactly what the repeated bout effect predicts with no intervention at all. Add the placebo response of a subjective pain scale, the regression to the mean of enrolling people on their sorest day, and spontaneous resolution inside a week, and an uncontrolled trial of anything will look successful. Soreness is also a poor proxy for damage or adaptation, and blunting it has never been shown to improve training outcomes.