There are two types of muscle soreness. Acute muscle soreness is the pain and stiffness felt in muscles either during or immediately following strenuous exercise. Delayed onset muscle soreness (DOMS), also known as muscle fever is soreness or stiffness that is felt 24-72 hours post exercise.
DOMS is caused by isometric or eccentric (lengthening) exercises, with eccentric exercises being the main cause of DOMS. Concentric exercises do not cause soreness. So, if you were able to completely do a workout of concentric exercises you would not be sore. However, this kind of workout would be nearly impossible to accomplish. While the exact mechanism of DOMS isn’t fully understood there are two theories that are most thought to cause soreness.

The first theory is referred to as the “muscle damage” theory. In this theory it is thought that there are micro tears in the Z-line muscle fibers of the muscle. When tears occur the pain receptors in the connective tissue of the muscle are stimulated and cause the sensation of pain.

The second theory is known as the “the enzyme efflux” theory. In this theory the micro tears cause a slowed cellular respiration rate which cause the calcium that is in the muscle tissue gets trapped in the cells. The excess calcium triggers proteases and phospholipids to break down and degenerate muscle protein. This causes irritation and inflammation which results in the feeling of soreness.

A third theory which has been refuted has to do with lactic acid build up in the cells. It was once thought that the buildup of lactic acid from exercise got stuck in the cell and caused soreness. It is now known that this theory is incorrect. Lactic acid levels return to normal levels within one hour of exercise and concentric contractions also produce lactic acid and it is known that concentric exercises do not lead to soreness

Knowing this, how do we minimize muscle soreness? There is an effect known as the repeated bout effect that states soreness will decrease each time the exercise is repeated. Another words, if you do the same exercises all the time your muscles get used to them and no longer respond with soreness. However, if you wait a long enough period of time (longer than several weeks) between doing the same exercise soreness can occur again. To avoid soreness you can repeat your exercise routine. However, this may lead to boredom so; perhaps a better way to prevent DOMS would be to gradually increase your intensity, reps and sets during your workouts. Warming up and stretching do not prevent against soreness. Contrarily, soreness can actually be caused by overstretching. A final consideration in preventing DOMS is nutrition. Proper nutrition may help limit soreness. With all these considerations of how to prevent DOMS, what happens when you over do it? How do you treat DOMS?

Generally anything that increases blood flow to the muscle should help ease soreness. This can include a low intensity workout, massage, sauna visits, or a warm bath. Cold water/ice baths have shown some effectiveness against treating muscle soreness, but only compared to doing nothing. Cold baths had no more effect on soreness than the previous mentioned ideas of getting more blood flow to the muscle tissue. Ironically continued exercise may ease soreness. Not only because it brings blood back into the muscle, but also because exercise increases pain tolerances/thresholds. Other things that may help include ibuprofen and gentle stretching.

Remember, it’s ok to be sore. It’s also ok to exercise when you are sore because you can’t do further damage to already sore muscles. The soreness should subside within 72 hours after it begins. If it doesn’t you may want to check with your doctor to insure you haven’t injured yourself.