DOMS stands for Delayed Onset Muscle Soreness, and is the technical term for being sore the day after you work out. It lasts for a few days and will go away. Basically, it’s a good way to tell if you have had a good, hard workout. The soreness itself is thought to be caused by the eccentric portion of workouts, which causes microtears in the muscle that need to be healed, which in turn causes the soreness. If we take bench press for example, the eccentric portion of the exercise is when you are lowering the bar to your chest, which lengthens the muscle fibers as you do so.