3 Causes of Sore Muscles: Injury, Lactic Acid, Adaptation

Muscle soreness can be caused by several factors. We will consider three of these factors in this article.


Soreness can occur because of an injury. When a muscle tears it is called a sprain. It occurs when a excessive force is placed on a muscle, more than it can hold, and the tissue tears. There may be pain immediately, or the pain may not be evident until a few hours later. The reason the pain may be delayed can be because during the exercise endorphines may mask the pain, or it takes a while for the swelling to happen which places pressure on nerves. The only cure for this kind of injury is plenty of rest, and cold over the injury. Continued use, or heat, or massage, will only make the injury worse.

Lactic acid

Soreness can also occur because of lactic acid. Lactic acid is a by product of energy production/break-down, in a situation where the body is obtaining energy from the breakdown of glycogen, as opposed to the use of oxygen. If the activity intensity level is low enough lactic acid will not build up because the body can get rid of it, or re-use it, at a rate equal to its production, e.g. slow jogging. During intense exercise lactic acid builds up because the body can not get rid of it fast enough, e.g. such as sprinting. Lactic acid causes pain and interferes in the contraction ability of the muscles. Lactic acid levels drop very quickly, within a couple of minutes, once exercise has ceased. To help the body rid of lactic acid gentle aerobic activity is usually performed. Excess lactic acid can be used to produce more energy or can be eliminated by the liver. Lactic acid does not cause any long term pain.

Microscopic cell damage

The kind of soreness one experiences 24-48 after exercise is believed to be caused by microscopic cell damage. The theory as to why it takes so long for this pain to appear is because it takes a few hours for swelling to occur, and for various chemicals to make it to the area to begin the healing process. The swelling and these various chemicals is what causes the pain. However, please note that this is only a theory, and nothing has been proven to show for sure why soreness occurs so late after the exercise. This kind of soreness occurs when a new exercise is performed, or when the intensity is increased dramatically suddenly. However, once a muscle is used to a certain intensity or a certain movement soreness should not happen again. The problem with this theory is that muscular adaptation can occur, which can only occur by damaging the microscopic fibers of the muscle, even though there is no soreness following the exercise. There is no known cure for this type of soreness. Stretching, saunas, warm showers do nothing to prevent or reduce the severity of this phenomenon.

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