DOMS: Delayed Onset Muscle Soreness
Why is it that the day after you go really, really hard during your workout, you can hardly move? The answer is the phenomenon of delayed onset muscle soreness or DOMS for short. When you work out or put stress on your muscles that they are not used to, you make little microscopic tears in your muscle fibers. Your body goes to work repairing these tears almost immediately after your workout is over. Repairing these tears causes your muscles to increase in size as well as strength.
But why does it take so long for the pain to set in? The answer to that question is a very hot topic right now. It was formerly thought that the pain was associated with the elevated levels of lactate in the body that occur during a work out. Lactate, or lactic acid, is the substance that causes the "burning" feeling in your muscles during a workout. However this theory is no longer accepted as the levels of lactic acid decrease very rapidly after about one hour of finishing your workout.
It is now thought that the type of exercise may be to blame for DOMS. Exercises that are concentric in nature, causing the muscle to shorten (the push-off part of bench presses) result it fewer tears, therefore less soreness. On the other hand, exercises that are eccentric in nature, causing the muscle to lengthen (the lowering part of a bench press) result in the most severe DOMS as they cause deeper and more severe tears in the muscle fiber.
So now that you know why you get sore, the question is how to avoid it. Unfortunately, you can’t. DOMS is a natural process that can not be avoided as it results from the tearing and repairing of muscle fibers. The only true way to avoid it is to not lift heavy weights. But of course, that just simply isn’t an option if your goal is to get your muscles bigger and stronger.