But lactic acid isn't the only culprit in DOMS. In fact, lactic acid is removed from muscle anywhere from just a few hours to less than a day after a workout, and so it doesn't explain the soreness experienced days after a workout. What is it then that causes DOMS for days after exercise? The answer is swelling in the muscle compartment that results from an influx of white blood cells, prostaglandins (which are antiinflammatory), and other nutrients and fluids that flow to the muscles to repair the "damage" after a tough workout. The type of muscle damage I am referring to is microscopic (it occurs in small protein contractile units of the muscle called myofibrils) and is part of the normal process of growth in the body called anabolism. It is not the type of damage or injury that you see your doctor about. The swelling and inflammation can build up for days after a workout, and that's why muscle soreness may be worse two, three, or even four days after a workout (it can take up to five days for muscles to heal completely depending on the intensity of the workout).