Scientists aren't 100% sure of all the causes of DOMS, but they have a pretty good idea. The burn you feel during the performance of an exercise is caused by the buildup of lactic acid, a by-product of exercise metabolism. It was once thought that the next day soreness was a result of this lactic acid staying in the muscle. Today, most exercise physiologists agree that the primary cause of DOMS is the tiny tears that occur in the muscle that as a result of high intensity exercise - especially resistance training.
When you work out, you literally "tear down" muscle tissue (these are microscopic tears - not like a "torn" muscle in the medical sense). During the days after the workout, the muscle begins to rebuild itself, provided it is allowed enough time to recover and sufficient nutrients are provided. This rebuilding process creates a "new" muscle that is bigger and stronger than before. In a nutshell, this is how the enitre process of muscle growth takes place.
This type of pain is different than the burn you feel during the workout and it is different from the pain of an injury. It's important that you develop the ability to differentiate between the "good pain" of soreness and the "bad pain" of injury. Unless the soreness is so extreme that it is debilitating and prevents you from participating in sports or performing routine tasks (like walking up a flight of stairs!), then next day soreness is GOOD PAIN! It is a sign that you had a good workout - that you trained hard enough to break down muscle tissue. As a result, your reward is going to be bigger and stronger muscles.
DOMS will be greatest in a beginner who has never worked out before. The more your body adapts to the workload you impose on it, the less soreness you will feel. If you continue to repeat the same workout over and over again, it will eventually cease to make you sore. Unfortunately, you will also cease to make any progress. Progressive overload is the cornerstone of getting stronger and building muscle.
Soreness doesn't just occur in beginners. No matter how many years you've been training, you may also get sore when you begin a new routine. Shocking your body and providing progressive overload are the keys to muscle growth. Each time you "shock your body" with a new workout program, new exercises, new techniques you've never used before or techniques you haven't used in a long time, you can expect the soreness to return. Be aware of this every time you begin a new training program or if you follow someone else's routine that you've never done before. Sometimes the amount of soreness just from a change in your routine can be incredible. Always go easy the first day on a new program and build intensity gradually or you're asking for it!
Negative repetitions, where you lower the weight more slowly than usual, also seem to increase the level of muscle soreness. It is believed that this portion of the repetition causes greater micro trauma to the muscle fibers than the concentric or lifting portion of the repetition. (Which, by the way, is a good reason to never eliminate the negative portion of your rep as certain exercise machines do).
What if you're still sore from your previous workout? Should you still train? If the soreness is very minor, then yes, go ahead and train right through it. As blood gets in the area and your body temperature increases, the remaining soreness will dissipate. However, if there is any substantial amount of soreness remaining from the last workout whatsoever, that is a sign that you have not completely recovered yet. Your body is still "healing." If you keep breaking down muscle before it has a chance to recover, the effect will be the opposite of what you want: you will get weaker and smaller.
Personally, I get sore quickly: 8-12 hours after a good workout, peaking about 24 hours later. I usually stay sore for anywhere from 2-6 days, depending on how severe the workout was. Me being the high intensity bodybuilding "freak" I am, I enjoy the feeling of not being able to walk for 5 days after a crazy squat workout - but of course, that's just me. I'm not saying you should follow my example - it depends on your goals. My goal is large, muscular legs.
As a competitive bodybuilder, I consider soreness to be an indication of a successful workout. I also consider the complete dissipation of the soreness as a sign of full recovery. If I feel no soreness whatsoever, I usually consider that workout as a mere maintenance session - if not a complete failure. My attitude is: I don't train to maintain, I train to gain. And if I'm going to gain, I have to get sore. Getting sore is one of my goals!
Not everyone will agree with me on this point (like those wimpy people who preach, "train, don't strain"), but there is scientific support backing my belief: In the textbook, Physiology of Sport and Exercise (Human Kinetics, 1994), Professors Wilmore and. Costill write, "Some evidence suggests that this process is an important step in muscle hypertrophy." There - case closed.
So, to get back to your original question; what can you do to alleviate the soreness? I would suggest that you shouldn't be trying to avoid it, you should strive for it and enjoy it! (at least a moderate degree of it). That said, there are a couple things you can do to reduce it after it's already occurred and it's a bit much to stand. You can probably reduce the soreness by stretching the body part AFTER the workout and by getting circulation into the area with cardio.
I've found that a short session of bicycle after a leg workout, followed by a vigorous stretch (especially when assisted by a partner), reduces the soreness somewhat (but don't expect it to remove the soreness completely). Other methods like massage might help as well. You can also cut back your intensity next time: Use your level of soreness as a gauge of your intensity. If your soreness is debilitating, then take that as a sign to back off at your next workout (if you don't want to be that sore again).
I don't know of any supplements that will help alleviate soreness and improve recovery. Proper post-workout nutrition will, of course, help with muscle recovery in general, but won't remove the soreness. That means making your post workout meal high in carbs, high in calories and moderate in protein. A complete discussion of post-workout nutrition will have to be the subject of another article.
Post workout muscle soreness is "good pain" in my book. If you are training with weights for recreation or sports, that's another story. But when it comes to muscle growth and bodybuilding, soreness is a goal to be sought after. The name of the game is to tear down the muscle, then feed it and allow it to recover so it can re-build itself bigger and stronger than before.
When people who know me watch me limp up and down the stairs or grimace in pain as I sit down into my chair, they know the story: "Leg day yesterday, Tom?" Those who don't know me and don't understand bodybuilding just think I'm crazy. (I've been called a "psycho" on more than one occasion - but I take that as a compliment.) Sure, I get some awfully funny looks at times when I'm hobbling around, but that's too bad - let them think what they want. When I can't walk right for 6 days after a squat workout, I know I'm gonna grow!